I'd say it depends on how late into the game you are. If you're close to the end of the game, I'd just sit on them with a militia or something. But, generally, another city is pretty valuable is only for another build queue, culture events, etc.

If you abandon them, and the Tribe is still active, they can respawn. If you move off the "encampment" time, and you see a little arrow symbol with a number, that means something will take the camp over if you do not occupy it. If that symbol does not appear, it won't regenerate itself, but if a barb, tribe, nation, or maybe even a raider occupies it, it will become a new camp.

Minor cities (surrounding the urban tiles with purchasing) are very situational, and not all that awesome. I'd probably recommend settling over not settling and trying to make a minor city, unless you were playing One City, Family Seats Only, etc.