You're looking at it all as one thing, sacking Poch and hiring Mourinho. They're two totally independent factors.
I think even the most optimistic of fans knows Mourinho has at best , 3 years in him.
That's got nothing to do with the absolute need to remove Pochettino from him role in November. If we had stuck with him, we would have been in a relegation fight. He had either lost the dressing room, or just stopped giving a fuck. He wanted out and he wanted the sack. No manager resigns when there is millions on the table for being sacked.
That issue with compensation needs to end. Clubs need to factor this into contracts whereby if unless there is a maintenance of form, there shall be no compensation for sackings. In no other profession can some one actively stop performing their duties and walk away with huge compensation. It's just ridiculous.
He will go to United. He will either be a success as they will certainly back him, or he'll repeat the same errors he did at Spurs. He will be there 5 years or so and then leave.
That is football now and has been football for 20 years with the exception of Fergie and Wenger.