You really think it is that simple and that a caretaker manager comes in and does a few training sessions and suddenly, by some divine magic, the wins start accumulating !
It will take at least one full winter and one summer window of clearing out some absolute dross in that team (defensive positions mainly) and a proper manager for United to actually close in on the top three.
Considering this season is very close to being an absolute disaster I think a top 4 finish must be achieved if we want to challenge next season with a new manager and a shiny new midfield if things go well.
Also I think with the squad we have all we need is a good enough coach until the end of the season to achieve it.
We have much better players than Spurs and West Ham for example.
This is just my version of best case scenario though.
The worst case scenario is that our board will keep panicking about what to do with this situation, we finish outside top 6 and in that case I don't think it's unreasonable to think Ronaldo will get very frustrated and will want to finish his career elsewhere.
Season like that would definitely destroy the atmosphere in the dressing room.
I just hope something will happen during the international break that will finally move this team in the right direction.