Not really. They are assets and you sometimes need to invest in them before you can flip them.
Neither will sign a new deal based on a interim managers views so you will get nothing for them. That's makes no logical sense. Why would either move in Jan for any fee when they can limp through to may and get even more money ?
So you paid them all year and get nothing back. I would imagine that would amount to a good 150mil in Pogba's case. Letting him leave for free twice is a utter joke.
This made sense years ago when wages were lower. In fact in the 90s I did this on Champ Manager all the time, sign players up on 5 year deals to make them worth more regardless of whether they would get many games for me. The max wage was £9999/week.
However the issue now is players like Pogba will be on mega-money. So if you sign him on a new deal, he will demand absolutely top whack, because he knows another club will pay him that much if they don't have to pay a transfer fee. Juve pay Aaron Ramsey £400k/week for this very reason, because he was a Bosman, so how much would they pay a higher rated player with prior experience of doing very well at their club Pogba? So then MU have Pogba tied down on a new deal but he costs ~£2m/month in wages. This then rules out a lot of options, not many teams can afford to buy him out of his contract at MU AND then also pay him the same wages. So there's a risk of it backfiring if you sign him up again, it's a Winston Bogarde situation but at 10x the price because of the escalation in wages since then.