Just seeing this forum thread for the first time:
I think most fish will come back.
They might realize how much money they save by not playing, but think of it like New Year's Resolutions. How many times has someone claimed they will go on a diet and lose some weight? Now how many have basically "given up" after just two weeks into the year?
Truth of the matter is that it takes more than motivation alone; change is often hard. Poker is the same way. Poker fish are the same; they usually enjoy poker like the rest of us (just not as successful at it). After a while, they may miss poker: give them a few weeks after it is safer to play live games again and I bet they'll be back.