Shigaraki’s decay is a whole lot like Vegeta’s hakai and you can also picture it being stopped by sheer power in the same way. Vegeta’s aura will protect him from any incoming attacks and Shigaraki’s abilities will be no exception. Vegeta can end the universe in an instant and there isn’t really a way to dodge that kind of attack so Shigaraki would really be taking the L on this one. Vegeta wins.