Into what form of energy is that mass converted?
I don't think much else would escape the black hole environment.
Tells me a bit darker thing in between the lines - the chance some advanced civilization (or us in far future if we actually survive) traveling FTL by bending space massively is next to zero, we would see (or detect soon) the evidence... unless they do it on planck-level of precision and self-contain all ripples. Nah, it really seems c is the ultimate barrier so far... depressing.
It’s enough “oomph” that we can detect it more than half way across the universe.