GCJ will survive because it provides a facility that doesn't exist in the standard JDK (i.e., ahead-of-time compilation).
Well, that would be a reason. But on the other hand, the main developer of GCJ is RedHat, and they may well not feel like continuing it now.
Kaffe will survive because it's BSD licensed.
Kaffe is GPL.
Classpath will initially try to survive by copying large amounts of original Java code into itself, but I suspect will eventually become irrelevant as patches for classpath-using applications become available to allow them to use the original Java class library.
Well, then you know more than I do. And I'm a Classpath dev.
Anyway, there's a good six months or so before we'll be seeing the classlib code from Sun. Yes, if we do continue development (or those who do) will probably be incorporating parts of it, but not large swaths of it. There are some fundamental differences in how the two libraries have chosen to solve certain things, and it's hardly a matter of cutting and pasting some code.
There's also a likelyhood that parts of Classpath are going to end up in Sun's libaries. There are actually things that Classpath does do better. There are also parts of the classlib that aren't going to be open-sourced because Sun doesn't have ownership. Classpath may provide the replacements for those parts.
But all in all, it's a big win for Classpath, regardless. We're getting what we wanted, under the license we wanted it. And we even got Sun to talk to us and ask advice before it all happened. (And judging from the details of their actions, I'd say I they listened well)