Example of my thoughts:
Mew used transform!
Pikachu is loafing around!
Mew come back! Go Ditto!
Take a rest, Ditto. Go Mew!
will mew stay in the form of ditto or go back to its original form?
No, It won't. Tested on Showdown!
Hope I Helped Ya!
nope wen u bring it back it back or when it faints it will automatically go back to its origial form