We have no clue about yaujta medical abilities, therefor we don't know if scar could still be alive or not.
Yes and he is if you look at my earlier posts he is coming back in AvP 3 redemption
1. Scar is dead, worm food - and with ahuge hole in his chest, so no Scar will not return, and
2. AVP Redemption is NOT a sequel it is a fan film...
AVP Redemption
scar is 100% and will never retourn