OH the extra work!!!
Months ago I started renaming all of my mon.
Prestigers have "!" as the first character, followed by who they were to be used against. So, my prestige team Venusaur(s) = !VapRhyTy, and my prestige CLoyster(s) = !Drag. (You get the picture.) This made it really easy to pick a prestige team. Sort by name, and all the ! showed up first in the list.
Looking today, I have over 55 mon named with the ! symbol. (Ok, I went overboard on keeping prestigers.) Now I have to rename all of them in order to get them to match the rest of my naming convention and show up where they belong. Damned Niantic, messed up everything! <<Sarcasm font.
Answers
I partially disagree! I don't think that CP is going to have to go all the way to zero for the mon to be kicked out. I think that the deciding factor is strictly the motivation.
From the press release: " As a Pokémon loses motivation, its CP will temporarily decrease, making it easier for opposing teams to defeat. To help keep the Pokémon motivated and in tip-top shape for their next battle, Trainers can treat their team’s Pokémon to some Berries, which restore their motivation. If a Pokémon loses all motivation, it will leave the Gym and return to its Trainer the next time it loses a battle,"
It does not state that CP will be the deciding factor for if the mon leaves the gym.