Yeah, I think that more people will leave the server, even without the drama-baiting the whole KISS thing has brought upon Gunnar's Hold. However, there is a pretty solid core of guilds and/or people that have declared that they will stay until the bitter end.
A community-wide migration seems not feasible, as moving one guild as a whole without it breaking apart is already very tricky (there seem to be a lot of such stories going around). Personally, I am one of the people who will stay with Gunnar's Hold, or rather, the RPS guild.
It is also worth noting that even when people decide to leave the server, they can still be part of a guild on another server. As far as I know there will also be expanded guesting implemented in future updates. Concerning the sever-hopping behaviour we have seen lately, both of guilds unhappy with a given community and opportunists that leave servers that are doing not so good in WvWvW matchups, I think that ArenaNet has missed the opportunity to stop that in time. That's a real shame.