MUI was saying: This doesnt look good. It looks like Vegetto's attacks didnt reach the whole area. So some pieces of Buu are still intact. But I hope Salagir will make this a bit realistic and make Buu greatly damaged after all of this. I mean this Majin punisher attack has been meant to vaporize every single cell of Buu. Even if some pieces of Buu are left atleast make him very damaged because he has lost a lot of his other pieces.

For example Buuhan was having trouble regenerating at the end of his fight against Vegetto because he took so much damage that he couldnt keep up anymore. Fat Buu could no longer fight and regenerate against Kid Buu. The same should be for Zen Buu. He should not have infinite health.
His power is far superior to all the other Buus, Honestly, he should be fine since absorbed so much of his universe but then again for the story to go anywhere we do need some plot devices to stop this God