Exactly. Once your object reaches the right radius it's done. It will 'evaporate' eventually. But it won't revert back.
An interesting result is that you could, and this is very much beyond our engineering, manufacture black holes like this.
An interesting result is that you could, and this is very much beyond our engineering, manufacture black holes like this.
The evaporation is a bit trickier, also known as Hawking radiation. It has not been observed yet, but it's one of those cases when we are pretty sure something like it must be going on. Otherwise we have even bigger hole in our understanding of the universe.
Theory is more difficult, but the practical effect is relatively obvious. Once the 'surface temperature' of black hole reaches over that of microwave background, it will begin to evaporate. The process is slow at first, but non-linear. As black hole evaporates, it loses mass, but the temperature actually rises.
Eventually, the process should end with a gamma ray burst.
There is a lot of unknown in that.
Right now we are very, very far from doing any of this. We would need to achieve much higher strength of magnetic fields before we could even consider this. It may turn out, that it's easier just to "catch" an existing micro-black hole. If they exist that is.
In practice, probably impossible, or at least well beyond our current technological capabilities.