I don't remember if this is still the case, but for most of D&D's history, killing a polymorph to target with force it to revert immediately back to its original form. This can be illustrated by reciting to you in old story I read once, as best I can remember it, from back during the AD&D 2e days.

Their once was a gnome illusionist in the party who finally got to high enough level to cast polymorph. So one day they encountered a hill giant, at which point gnomey busts out his new spell, trying to polymorph the giant into the least dangerous thing he could think of - a grape. The giant failed his saving throw, after which he was turned into a grape. The gnome cheerfully picked up the grape, saying "I like grapes!" and popping it into his mouth to bite down on.

Kersplort.