Beerus' Hakai would probably prevent that even if he let his guard down.
For the sake of the thread and assuming Boo succeeds entirely, it likely alters his personality to somewhat becoming more intelligent and having some level of Beerus' memories, given his dominant nature and Hakaishin status. Whis likely takes Boo away to train him as a Hakaishin to utilise Beerus' power properly. Goku and Vegeta don't get the opportunity to show their potential to Whis, receive no training and they are killed months later by Freeza, who assumes his position as ruler of the universe afterwards.
The U6 tournament never happens, nor does the Zero Mortal Plan or Tournament of Power. The most that would happen as far as continuity from then on is perhaps Hakaishin Boo VS Broly. An unspecified amount of time later, Universe 7 is erased by Zen-Oh along with the other lesser universes.
