I had a crazy thought. I made a ginormous stout that came out more ginormous than I thought it would. Bottom line, I need to pitch more yeast. What if I collected some yeast from the fermenter, threw it in a starter and re-pitched into the same beer?
If you could choose between a fresh pitch of yeast or reusing, I’d use a fresh one to work in a high ABV environment. The reused yeast may do OK, but fresh yeast may be in a better position to do what you’re asking.
I agree with jverduin. If the yeast petered out before fermentation completed it’s likely stressed and not a good candidate for reuse.
I agree that the preferred route is fresh yeast, but a starter that is new with a dose of the old slurry is really awfully similar to a starter of new yeast that has finished and settled out within the starter. But, regardless, I would pitch it at high krausen for either approach. Look into an Shaken not Stirred starter and pitch it at high Krausen and I bet you will get some downward movement in the gravity. Just a guess - nothing science based in that.