Those are protocols, so the servers/services that run than can come and go. XMPP, which was at least inspired by ICQ, will probably be around forever, similarly.
OSCAR is a protocol too. And there were ICQ servers to run locally back then too. There also was some "ICQ for business" or similar.
I've also learned yesterday that people responsible for Escargot (MSN server) have another project, NINA, for AIM and ICQ.
So maybe these things will be reborn.
They seem to aim for implementing all of the AOL suite functionality. Maybe after they achieve that we'll see Xtraz and contact directory from ICQ working again. If that happens, I'm going to cry for a few hours. EDIT: or weeks.