What happens when a non-token creature loses all abilities, is exiled, then returns?
Polymorphist's Jest does not create tokens, it only changes the stats and characteristics of the creature's controlled by the targeted player. It is still the same game object as far as Magic is concerned.

Under the circumstances presented in your question, your opponent's creature would be 'flickered' (magic slang for exiled and then returned to the battlefield) and when it returned it wouldn't be a 1/1 frog anymore, it would be whatever the face up of whatever card was returned.