I mean if Smith-Rowe breaks down we still have all those players Arteta went into the season with who aren't good enough. We're just better off for having him playing a lot.
If ESR hadn't broken through and we went and signed someone in January we would still be stuck with those players as backups too, and that's assuming the signing would hit the ground running - but as we've seen with Pepe the opposite could easily happen too, and then we have to spend years trying to get them to function within the team instead. Or they could be satan in disguise like Willian. There's cost and risk involved in every decision.
Right now we have a working player and that's why we should keep backing him. It seems like the least risky short-term option to me, and then we can see what might be achieved in the summer. I also think the fact we're so blatantly better off with a playmaker shows quite clearly that, whatever people think of Özil, it was a bullshit move to leave him outside the squad. You need players like this if your attack is going to work.