I think Kreatious will be around until Minecraft fades out. To be honest, it's been around a lot longer than I would have ever anticipated! As anyone who has moderated the server knows, it becomes a chore after a while. With little time to build for yourself, and constant interruptions from players, your buildings take a back seat, and the community takes the lead. But, such is the price of being a mod...to make sure every other player can enjoy wonderful buildings and ease of mind that the community is in check.
The reason I say all that, is because despite that fact, Zerg continues to log on frequently, after what, a half decade of being in charge?! It may not have 70+ players on at a time like it used to, but it has enough for the community to function. It's a unique server, and that's what will keep people coming, when the other ones close down.