1. Yes I probably would, or rather I would want to sacrifice a limb in order to survive, but unless I was in the actual situation I can't really give a qualified guess as to whether I'd be able to go through with it or not, I'd likely attempt to do it, and if I couldn't I'd attempt suicide, I prefer spending a few agonizing minutes by my own hands to whatever slow death I might encounter like that.
2. Depends, if they are people I really care about and want to give the best possible chance of survival I'd likely go for suicide so I wouldn't slow them down. Missing an arm would make me about as capable as a pack mule and would require lots of time to train myself in 1-handed everything, and a leg would be even worse, depending on how our situation was supplies/shelter/people/food wise I'd only want to live if I knew the group could support me without compromising the mobility/safety of the others.