obviously if I cast {sudden spoiling} and then {drown in sorrow} everything will die, but what about the reverse? Do the creatures die or does sudden spoiling negate the -2/-2 effect? And what about with damage like {anger of the gods}?
Yes sir. The damage and -2/-2 effects wear off at end of turn. Which is why you can counter an alpha strike with {Circle of Flame} + {Polymorph's Jest}. They take the damage, become 1/1s and die.
Either way, they die. That's because the base p/t is applied before the -2/-2 effect, no matter when either started to take effect.