If you think about it, it's quite impossible for Barcelona to buy him if he doesn't show good performance. His sales are still quite high for Barcelona and he also has a high salary, while Barcelona doesn't have stable finances. So I think Barcelona management is only borrowing him for this season as a substitute option and Barcelona has no real intention of buying him.
And I think he will also only get limited playing time, considering that Barcelona already has capable main players he will probably be used when Barcelona player are injured.
If the conditions are like this then it is not very good for Rashford's career in the end because if indeed Barcelona's scheme is only to use Rashford for loans only then the situation will not be much different from Joao Felix who has experienced something similar before.

For Barcelona maybe this can be profitable but not with Rashford especially when his performance does not develop back in a better direction. So by looking at this, it would be better in the end for Rashford to now show his performance and as much as possible make Barcelona want to make him a player for the long term according to the loan option to buy at the end of the season.
This would be to his advantage although there may be some issues such as salary that could be held up (as it is a classic Barcelona problem) but at least he should get a place first to create momentum in his return to form.