They're not officially supported, that's not to say that if huge problems arise that compromise the integrity of the games there won't be some unofficial support. The 1.09 patch for CE and PC was released after the official support was dropped, and so was 1.08 to my knowledge. These both fixed issues that people could use to maliciously crash specific servers though, I don't see anything except critical support like this in the future.
Gamespy threatened to stop supporting the master-server list awhile back but reassessed that and continued support. Due to this, there have been a couple projects from community members to provide extended master-server support if this server happens. I know of one master-server project that currently works 100%, and will also allow people running multiple servers to make clients attempting to join full servers join another one of their servers with space. There's also plans to allow Halo Custom Edition clients to download custom maps they don't have from the server directly without having to restart their client.
Have no fear, Halo Custom Edition (at least) will live on! Halo 2 Vista was garbage though, so I honestly don't care what happens to that game. On that same note, there's no reason for all the people playing Halo 1 PC online not to be on Custom Edition... So if this community supported master-server ever takes off it'll probably just be for Custom Edition.