In fact, it would be the right decision, another thing is that it is simply impossible for financial reasons. United (like probably any other club) cannot afford to change the team entirely when changing the coach. Therefore, United are expecting targeted changes that will gradually lead to the team that Amorim wants. As for selling/renting players, I don't think there are many options. Who needs Rashford with his salary? PSG were after him before Ten Hag.
Sadly, MU owned garbage management who could not explore the loopholes like Chelsea. They were overconfident with their current roster. I know they have won 2 trophies, but can't really deny the fact their current roster is garbage now.
Things are changing so fast, and never expected them to go down even deeper to the out of top 10 EPL. They have tried to put some of players to sale in the last summer window, and they rarely got offer for their players. It seems to me they have to start from the scratch.
So I think that a serious rebuilding needs to be done for Manchester united to get back to their feet again.