2014-11-24 : If a creature was dealt damage but regenerated (which removes all damage from it), it will still be a legal target for the second mode of the triggered ability.

2014-11-24 : If a mode requires a target and there are no legal targets available, you must choose the mode that adds a +1/+1 counter.

2014-11-24 : You choose which mode you’re using as you put the ability on the stack, after the creature has entered the battlefield. Once you’ve chosen a mode, you can’t change that mode even if the creature leaves the battlefield in response to that ability.