Hungry black holes trapped in an intimate dance feast on leftovers from a galactic merger

I wonder how disruptive the merger of 2 supermassive black holes will be to a galaxy.

It seems like there could be more energy involved than anything else we have observed or contemplated so far.

But, how much of that energy escapes, and how much ends up getting swallowed-up into the resulting single black hole, without letting much blast out into the surrounding stars?

Anybody know of a predictive model for this?

We may get a chance to actually observe such an event in my remaining lifetime. See . Glad it is 1.11 billion light years away - don't want it shortening my life.