Well, I am unsure exactly what you mean by at what point do they become mini-big bangs? As soon as an object becomes a black hole, it starts releasing
these particles. And remember, it's not "creating" mass - it's changing energy to mass. When the black hole reaches 0 mass, it seems to simply
disappear - as if it winked out of existance. A black hole would not continuously grow if left without nearby matter, but would slowly shrink. Of
course, if something with matter does come around the black hole, it'll consume part of it. Since there's a lot of cosmic dust and whatnot, it's
unlikely that a naturally occuring black hole will fully disintigrate (at least, not until the universe is immeasurably old and all matter has already
been consumed, and black holes exist universes away in distance). However, it does apply to microsingularities that we have created... thankfully.
Now, onto M-theory. When you mentioned it, I had not ever heard of it, so I decided to do some research (god how I love Wikipedia). M-theory is
looking for a way to unify all the string theories that exist. String Theory itself is something that tries to tie together General Relativity and
The problems with General Relativity and Quantum Physics is that GR can explain things on the universe at the large scale, but sometimes messes up
when working with the fundamental building blocks of the universe. QP, on the other hand, works perfectly well for describing what happens on the
atomic level and smaller, but messes up when trying to explain things on the large scale. String Theory tries to unify these.
Problem is, there's a number of different String Theories - and some of them are right some of the time, and others are right at other times.
M-Theory is trying to unify them by finding their underlying base, something called Underlying String Theory (which is then called M-Theory). M-Theory
attempts to do this by finding where the mathematics, outcomes, or description of outcomes in the same - finding out where the theories agree - and
then simplifying it into one theory.
So, yes, I guess you could say it's Einstein's Grand Unifying Theory - but it's extremely complicated, and requires concepts that weren't around
in Einstein's time.
At the end of the Wikipedia article, it talks about Matrix Theory as currently being promising in completing M-theory - which I can only imagine works
by seperating the different String Theories into a kind of descriptive or situational matrix, which could then be manipulated to find which theory
would be used to which case. I do not know.
Like I said, we're getting into massively complicated and high-math subjects, which also include things which I know little or nothing about
afraid that if you go much farther with questions to every post I give, that I won't be able to help!
Of course, elaborations on Black Holes I will be happy to attempt to explain.