O'Shea for all his faults is not (entirely) stupid. He has to know that his track record for the past 3 seasons was damning and if he wasn't going to be fired this year,, given his personality, it would be next. There is a saying that if you are at the edge of a cliff, if is better to jump than be pushed- you have a better choice of where you land.
I an and have been convinced for some time that O'Shea's time here was done as he had become a liability. I am waffling about Walters. If he was privately dissatisfied with O'Shea and was engaged in a lost-lose-lose power struggle with O'Shea, then perhaps, with O'Shea gone, he can right the ship. My gut says that was likely the case. Nonetheess, if he leaves, clearing the decks might not be a bad idea.
Sempre avanti!