To make it more simple, just put the new IP on the forum homepage in large bold letters, so if someone doesn't know the IP, they can just check the forums.
I see no down side to going back to the old domain except changing yet AGAIN which if you think about it...
The reason we lost our player base is because only a minority of us even acknowledge that they exist.
I mean for mntm you had to have a forums account to know it existed, so you would most likely know the new one. Of course, if there are any stragglers, it could be useful for them if they haven't found a new server yet.