As long as we don't get a new striker, he'll play. People can talk about Rashford as striker, and he's still better than Ronaldo as striker. But he's atill as average as a PL standard can be in that role. I even think he's championship level at that position.
It's been on record that Rashford has a fragile mentality when things don't go his way (see McClaren's and with your own eyes). Which is often happened when he played as striker. And the coaches are trying to build up his confidence this season, and he has shown a lot progress in his play on the wing. You don't want to damage that again. So it's a catch-22.