I agree that Bruce may change his mind. So many actors state that they are retired (not necessarily from a particular role, but from acting entirely), then they come back. I believe Bruce when he says it, but I also think it's a bit foolish (or deceitful) to say 'never'. Sometimes he used the word 'never', but in his official statement on the matter, he used the word 'retired', which can lead to being unretired. We'll see. If the right opportunity (a good offer and script) presents itself at the right time...
Also, his reasoning is kinda wonky. He doesn't want to be in the blood and uncomfortableness of being Ash, he claims. But, my argument, is 'Why does Ash have to be in blood?' And Bruce is a producer, can't he make that call to not have Ash get such abuse? There's more to the character than splatstick.