As a vampire and with twelve fully iron armoured companions, I had a hard time taking out a vault. The unarmed ones were an even match for me, luckily, I had my companions. Warning: Even if you aren't legless right now, get a crutch. You most likely will get some leg damage. If you're able to play as a human civ, trade with dwarves to get as much steel as possible. Make a ton of steel armour and leather layers to go over this, for as many companions as you'll be bringing. For you, I suggest:
1: Get 2 steel mail shirts, one steel breastplate, a steel helmet, a pair of copper shields if you cant get artifact shields, steel chain leggings, steel high boots, five leather hoods and cloaks, leather mittens, leather socks, a leather long skirt, and a leather cape, plus your weapon, which must be artifact. All masterwork or artifact.
Optional: Get adamantine picks, spears, short swords, and battle axes from a former dwarven fortress.
Use the same amount of stuff, but with only one shield, and can be superior or exceptional quality level.
2: Swim, climb, grapple, anything with macros that increases your strength, endurance, and agility. Throwing iron picks as a legendary thrower can really be helpful.
3: Become a vampire. This can be surprisingly easy at times, or exceptionally hard. It is a must though.
4: Make sure everyone is as strong as they can reasonably get. Do a lot of fighting, such as ripping into a dark pit, to get their skills up. Spit at them, to raise dodging skill.
5: Approach carefully. Do not engage more than one at a time, and do so carefully. Don't rush at them, throw picks and war hammers at them and let them close in. Once they're within range, fight carefully. I suggest possibly getting a dwarf companion or two, as their martial trances are good.
6: Whatever you do, DO NOT engage the Archangel unless you and all your companions have divine metal equipment on. It doesn't have to be full coverage, just don't expect to survive otherwise. And pray that he's not made of metal.
Of course, even with all that preparation, you still face a good chance of being slaughtered on sight.