Pokémon phone home?

not sure sorry, BUT im sure i read/heard they need to be actually defeated by an attacker...

so they may sit on empty Motivation/low CP untill battled.

hopefully this gives us chance on actually staying in gyms over night....lets say the next morning a friendly trainer comes by and feeds all the starving defenders xD (or....its a trainer on a different team and he wipes the entire gym no problem :S)

https://support.pokemongo.nianticlabs.com/hc/en-us/articles/115009004687

The mons of left alone and not fed berries will lose motivation and be returned to you.

"If a Pokémon’s motivation is completely depleted in battle, it leaves the Gym and returns to its owner THE NEXT TIME IT IS DEFEATED."
Taken from niantics support page. Keywords are in caps lock. Hope this helps.