This is a really good question and something that worries me too.
If Trion doesn't shut the server down, then the life of the game (for me) depends on which updates the team decides to implement. If they stop at 3.0, I'll continue to play. Although the 3.0 update did a lot of harm to the game, it was still playable.
But if they decide to update to 3.5, then sadly, my time in ArcheRage will come to an end (just as it did in the official game). Because 3.5 is not playable (at least, not for me)!
As for spending real life money, I've decided to look at it as a subscription. I'm on a very tight budget, so I'll probably spend $5 a month. I consider that good value to play a game I love. But I'm going to wait a bit before I start spending, just to see if the server is going to stick around
.
But I'm realistic, I don't see the game lasting forever. I think the others are right, 6 to 8 months seems to be the life span of a server. But if they implement too much P2W, then that life span will be even less.
But as I said, for me, it all depends on which patches we get.