a) There are plenty of ways for a GM to fudge an accidentally overpowered fight without actually fudging rules or mechanics; I once recovered just by provoking extra opportunity attacks.
b) @ObliviousSage is right; in most D&D-type games, PC death is a risk that *must* exist in order for a challenge to be felt. The only way around this is to provide non-death risks. D&D doesn't support this innately, and it takes a creative GM to make it work.