Well, that depends if you want to have fun or to run a real life campaign. It might be a good idea to ask your players just that.

I normally try not to kill PC, but they do get a fair warning if they are going into a situation that is well over their heads and in that case if they still choose to proceed, then I let the dice to do the talking and what fair is fair.

But once again, I think the important part is what do your players expect? Do they want to play a Phoenix Command style game (where you do not show up without a dozen or so on ready characters) or do they want to play the Diablo style game (where one hero takes on the legions of hell single handed)... or is it something in between....

Kind Regards
Daniel