Converted into energy and then escape the black hole, from which light can’t escape? That doesn’t seem to compute. And if it’s converted into gravity waves then we have an excellent obvious candidate for how most energy will escape a black hole. It won’t be waiting around for hawking radiation.
I think during the merger the event horizon must be changing rapidly, so I guess there's some(or a lot) of chance that matter can escape these merger events. The matter will already have high kinetic energy...
