Now the most important question is at what point does this take place in the respective universes. For maximum funzies, I am going to assume it is at the very END of their respective timelines. IE: Post Throne of Bhaal, and about 10 seconds before Scar is zombified by the emmission at the end of clear sky. Thus, each is at his peak.
Cuz if this is during or post Throne of Bhaal, then Minsc is a lvl 30+ ranger. Able to cast decent healing spells, but most terrifying for his epic level abilities (It is worth noting that once epic level play starts, it is pretty much guarenteed that said epic level D&D char is on their way to godhood. Not major godhood perhaps, but godhood nonetheless.) and awesome magical items. It largely depends on how the player of the game decked him out, but by the end of my ToB run, Minsc wielded the +5 flail of the ages with a +2 tower shield(+4AC in melee, +8 vs ranged), and was clad in +5 full plate(15AC), belt of giant strength (the 22 one) and had the helm of baldurn. Very important that helm, since as fuzzy zergling said, all chars use their own universe mechanics, and this helm PROTECTS AGAINST CRITICAL HITS. IE: headshots. It also adds another +1 to ac. So by this point, minsc's AC is -15, (Minsc gets +1 ac from dex for those keeping track. his actual dex would give more, but that is the max for when wearing full plate). For those of you not familier with 2nd ed. mechanics, that is a 35 AC. meaning that minsc is as hard to land a blow on as the TORRASQUE, the monster designed by the devs to be the ultimate invincible challange beast. Since minsc operates on D&D mechanics, that means that any shot by Scar that doesn't pierce armour, does 0 damage. Sniper rifles in D&D d20 modern do 2d8 damage per shot, for the low caliber ones(Vintar), 2d10 for the large calibur rifles(Dragunov), 2d12 for an anti-material rifle (Which the Gauss Gun would qualify as) but remember that minsc is at epic levels by this point. He has a couple hundred hp. As far as Minsc's damage capabilities go, remember that belt? This is not 3rd ed D&D where 22 str is only somewhat better than 18 str. 22 str is enough to pick up and throw a car. (side note: minsc's unbuffed str is 18/96. This is herculean.) Using D&D mechanics, this not only gives minsc an INSANE bonus to damage, but it also adds to his ability to land blows. He has 8 attacks per round, just under 1.25 attacks per second, and each blow comes with the strength of a storm giant, and has a +5 magical attack and damage bonus as well as each of the flail heads adding a unique type of damage. (+2 of each fire, cold, acid, electric, and poison) The flail also protects from movement impairing effects and has 5% magical resistance. Given that STALKER armour needs to be proof against the anomolies of the zone, I would say that Scar's armour would protect against half the bonus elemental damage that the flail does.
On the Scar side of things. Since we gave minsc end of the game stuff, asssume we do the same for scar. Fully modded exoskeletan as used in clear sky, modded for maximun resistance to gunfire. For anomoly hunting, assume he uses a thusly fully modded SEVA suit. Thats what I and everyone I know who played the game did at any rate. For a weapon, we see in the starting cinematic that scar favors a Vintar, but due to it only haveing 2 small tiers of customization where most other guns had 3 large tiers, the Vintar in clear sky is somewhat underpowered. I shall assume that Scar carries the loadout I did, maxxed SPAS-12 for close range zombie/mutant killing. buckshot is ideal here. rate-of-fire modded TR-301 for mid range work, the thing was basically a minigun with a scope. Vintar/Gauss rifle for sniping. Enough dakka for any situation. We should like to think. Scar also has a worthless pistol slot and a combat knife. Since this is clear sky rather than SoC, the knife is merely a decent melee weapon rather than a vorpal keen blade of annihilation. For artifact loadout, assume a collection of radiation reducers, a bleeding stauncher, a healing one, and since scar could scope out his opponant with his scope and see what he is facing, a couple and reduce rupture damage (slicyness). Assume that he is in his exoskelli cuz he goes in expecting combat.
How I see this playing out:
Scar: "Just another contract." BOOM, HEADSHOT via gauss rifle. Which bounces off the magical enchantment of the helm of baldurn. "Well, shit." Being the intelligent and expert STALKER that he is, Scar switches to his vintar rather than wait for the 10 seconds for the gauss rifle to recharge. During this time, Minsc has started across the bridges toward his enemy. Scar takes aim for a face shot this time, below the protection offered by the helm. The shot is a hard one to get what with a moving opponant who is interjecting his MASSIVE shield, but scar is one of the best snipers in the zone. The discharge is more of a SNIKT rather than the thunderclap of the gauss (silenced gun, subsonic rounds), and half of Minsc's face disappears in a spray of red, but he pushes on. Massive head trauma does not matter. HIT POINTS matter, and minsc still has over 100 of them.
Swearing as he sees his mark ignore what should be debilitating injury and hemmorraging, Scar realizes that Minsc has closed to just one bridge away. This is too close for sniper work, and besides, he now has that collossal shield between them, so precision aiming at a vulnerable location is right out. As minsc charges, Scar pulls out his rapid fire TR-301 and empties the entire 45 round clip in just under 4 seconds. The bullets all impact the massive tower shield, and its protective magics are not proof against this much damage. The shield comes apart and minsc takes a score of rounds to the arm and chest, but these are still clad in +5 full plate. This magic is far more formidable and shrugs aside the gunfire like rain. Moments before entering melee range, the ranger throws something and screams:
"GO FOR THE EYES BOO. GO FOR THE EYES!"
Scar is backpeddaling as he hurridly pulls out his weapon of last resort; the SPAS-12 with alternating buckshot and slug rounds for mutant hunting. The buckshot will be worthless he realizes, but the slugs might be just enough to penetrate the incredible armour of his foe. As he backpedals while firing, he unknowingly trods on a small rodent.
Minsc, upon seeing Boo crushed under the exoskeleton heel of his attacker, goes berserk. He gets +2 to his Str, bonus HP, but -2 to AC and wont stop attacking regardless of tactics or safety until the rage ends. He swings the Flail of the Ages in a whirlwind of blows, each as strong as if swung by a giant, and ignores the rounds being pumped into him, what few that get past his near-invincible armour. Scar is unable to escape from melee range due to the exoskeleton's inability to sprint, and is forced to endure the onslaught of blows. The exoskeleton is a fine piece of armour, but not proof against the eldrich energies and inhuman strength being plied against it, and after a number of blows, Scar goes down. Minsc keeps pummelling the corpse till all that remains is a pile of blackened meat and bits of kevlar, metal and a spreading pool of hydraulic fluid and blood.
After the fight, minsc is near-crippled with wounds, but he does know some low level clerical magic (enough to ensure that he will not bleed out), but alas, Boo is no more. We pine for you Boo. WE PINE FOR YOU!