Kinda depends on what you call "dying", really. Orks are more resilient than Necromunda humans, both because they have base Toughness 4 in a world that still contains a lot of Strength 3 attacks (it's based on 2nd Edition Warhammer 40k, and fudged for campaigning, so most guns have Strength 3), and because the rules give your Boyz a lot of chances to shrug things off without too much permanent injury.
But it's definitely Warhammer, and the dice can totally screw you over. In that test game I played, my Warboss lept out of a moving vehicle and failed his landing roll, then failed his Toughness roll, taking him Out Of Action. After the game, I rolled his Injury table, and he got the "roll d6 worth of injuries" result, which left him at Strength 1 and toothless.
Point is, don't get overly attached to anybody, but for the most part, Boyz will usually live on battle after battle. And even if they don't, the game quite explicitly gives you the option to fold your Mob and rehire any particular members you want to keep into a new one.
One rule that will be important in a campaign, and especially so if you want to play by Vassal, is that you always have to have enough vehicles to carry your whole mob. How many Orks can fit in a particular vehicle, you ask? "As many as you can stand on the model without them falling off," says the rulebook. So basically, any group that wants to play Gorkamorka on Vassal has to come up with some ground rules about how many infantry models the three kinds of vehicles can carry.