I agree that it would be bold to let Rashford, Ronaldo, Martial, Lingard and Cavani leave in the Summer; especially with the Greenwood situation.
However I think we need to think about the situation carefully. His contract effectively runs out in 2.5 years which means a couple of things. Firstly if he isn't sold in the summer then he's entering the final year of his contract the following year, which would adversely affect his value. Secondly his next contract will likely be expected by him to be the biggest of his career.
We're in a very similar position with Rashford now compared with Pogba just before Covid. High earning, under-performing player coming up to the supposed peek of their career where they'll be expecting a 5-6 year contract worth somewhere in the region of £100m; but their performances are light years away from their salary. The same arguments were made for keeping Pogba then; and now we're in a position where we've lost out on at least £100m of transfer fees/wages due to a misguided belief that getting rid of him would have weakened us too much. I bet most people here looking back would have sold Pogba for £65m back in January 2020, saved £35m in wages since then and replaced him even if that lead to an element of short term pain.
Even if the aforementioned 5 players left are we really saying given what they're currently bringing to the party that we couldn't find a couple of attackers who would work harder and bring more to the table for the cost? Hell a lad promoted from the academy several months ago on a tenth of his salary has quickly taken his slot and shown him up.
Would going into the season with a new striker, a new winger and Sancho, Bruno, Elanga and maybe Amad be any worse than what we have now (especially if we get a top level holding midfielder as well)? It would certainly send a message that Man Utd doesn't tolerate lazy underperformers irrespective of their name/talent.
It's a tricky situation due to the contract issue that you mention. That's a whole other issue within this situation that will need to be resolved. It's also a long-running problem that the club has with giving out huge contracts to players, or letting things run, which we could argue about in its own separate thread, too. However, I don't think just getting one striker and one new winger would be anywhere near enough. We would seriously need to be looking at least 3 new recruits, probably four actually in that attacking department. Considering that our recruitment has been very hit and miss over this last decade, we're asking for an awful lot to be done in one window. I'm not confident at all...
Elanga has shown great promise this season and Sancho has been putting in the performances lately. But, over the course of a season, you are going to pick up injuries, playing are going to be fatigued, and there will no doubt be dips in form. When you start throwing those things into the mix, that's when your squad depth gets truly tested. We really can't be going into the next season short of people, if we can help it. Let's not forget that this United team was tipped at the start of the season to be making some sort of title challenge, or at the very least cementing that top four position. Considering all of that, we have really fallen well short of expectations. What we don't need to do is further weaken the squad going into next season. (although, saying all this, Rashford is really taking up a squad position at the moment with his lack of contribution, so there is that)
For that reason alone, I can't see Rashford leaving. If he does go, the club has to be absolutely sure that they've got the replacements lined up, either through a transfer or through promotion of the academy. To be completely truthful, Rashford's performances this season have put off a lot of his fans, so I'm not firmly in the 'we must keep Rashford at all costs' camp at all. I'm more in the 'just make sure we've got a decent squad' area.
As you can see, I'm torn on the issue. The easiest thing for everyone is for Rashford to find the form needed and to put the performances in + start scoring. If this happens, then suddenly we haven't got a problem. But, it just isn't happening.