Team Jeff!
It wasn't so much that Jefferson was all aboard the Quitters Express. He was just selfish enough to want more to keep those around him alive than close this rift, especially when it seemed to let out more demons. More demons meant a greater chance of getting overwhelmed and impending death.
Such as Mary Margaret getting impaled through the stomach.
No amount of reoccurring death and not staying that way lessened the blow of watching someone's life get taken away. It was never something Jefferson particularly cared for -- at an earlier point in his life it was easier to ignore it, but not now. Not Emma's mother who had more or less died because he had some stupid mark thing to play along with another game this world had to throw at them, and was unable to protect himself.
Time had paused only enough to be hit with the reality of what had happened. He let the rift pull at the mark once more, this time the surge of energy sealing it completely, a large crackling pop as the tear dissipated, leaving only the remaining monsters in their wake.