Turns out you asked a question that even scientists don't know the answer to!

To really understand what happens, you would have to solve some very complicated equations from Albert Einstein's theory of General Relativity, but by making some approximations and using supercomputers, physicists are starting to think they have a pretty good idea of what would happen if two black holes collided.

Whenever two bodies (planets, stars, black holes, or anything else) get close enough to each other in space, they start to circle each other in some sort of orbit.

General Relativity predicts that when two black holes (which are very very massive) are in an orbit like this they will generate something called "gravitational waves" (which are like ripples in space-time). Gravitational waves are pretty complicated to explain, but in the end they basically carry energy away from the orbiting black holes which makes them get closer and closer to one another with each orbit. When the orbit eventually gets small enough, the two black holes would merge.

The only things scientists can say for sure about black hole collisions(after doing all kinds of simulations on their supercomputers) is that when two black holes collide they will form a single, more massive black hole and that there will be a huge burst of gravitational waves.

There's research currently going on that will try to make it possible to detect the results of black hole collisions. Hopefully in a few more years scientists can know the real answer to your question!

Hope that was helpful (and not to confusing...)! ;-)