There are 4 US servers now, but only one with a healthy population - Badlands. It's too healthy and over-crowded at times. Mythic recently disallowed character transfers to Badlands, so business may pick up on the other servers.
I think the game is safe from going belly-up...at least for the time being.
The realm vs realm makes it a real juggling act to keep not only enough people, but not too many people and also fairly balanced numbers of people on any individual server.