Hawking radiation.

https://en.wikipedia.org/wiki/Hawking_radiation

"Hawking radiation reduces the mass and rotational energy of black holes and is therefore also theorized to cause black hole evaporation. Because of this, black holes that do not gain mass through other means are expected to shrink and ultimately vanish.

For all but the smallest black holes, this would happen extremely slowly. The radiation temperature is inversely proportional to the black hole's mass, so micro black holes are predicted to be larger emitters of radiation than larger black holes and should dissipate faster per their mass."

See also: https://arxiv.org/abs/0908.1803 "Are black hole star ships possible?"

> black holes that do not gain mass through other means are expected to shrink and ultimately vanish

I agree with the first half but not the last. We know that the methods used to predict Hawking radiation are no longer valid in the regime of tiny black holes (curvature becomes extremely high near the event horizon but Hawking's computation assumes near-zero curvature), so the claim of black holes vanishing is a guess at best (and one that leads right to the black hole information paradox). Another option would be that we'll be left with a black hole remnant. Or maybe something else happens. Without a quantum theory of gravity we can't possibly know.

I know about Hawking radiation, but it depends on the thing emitting it to have something to emit and a lower energy state to enter. What are those for a black hole electron?

A single positron, I guess. Evaporating completely in one step. I may misunderstand hawking radiation, but that's the only particle I can think of that's <= an electron in mass. (I don't think photons count)