Stargate Universe ended quietly with a “the journey goes on...” pause before a third season that never came, but provided a kind of closure in its continuity.
SGU was pretty openly influenced by Battlestar Galactica, which provided such an ending in case the 2009 Writers’ Strike went on too long, but then came back for a final flourish complete with half an hour of quiet, bittersweet LOTR style codas and a final WTF moment following on from the season three cliffhanger WTF moment. I know it outraged some people, but compared to the end of, say, LOST, it was pretty good at tying together some wildly disparate threads (several of which I was less than keen on, but never mind) so my only real issue with it was one of staging which I found rather distractingly amusing.
There’s a lot to be said for having your characters ride off into the sunset - just as there’s a lot to be said for a clear finale.
I find the most reliable method is somewhere in between, a lesson taken from Buffy. (Many of my lessons come from Buffy.) Every year they provided and completed a seasonal arc, in case