A few things I’m thinking..

There are probably a million ways a reversal could happen (fusion, fission, eternity) that we don’t understand. Again about black holes, what is after the black hole, when the black hole dies? How did the ‘big bang/beginning’ start in the first place without anything?

Don’t know if the laws of thermodynamics would be counteracted, or if other laws we don’t yet understand would prevail.