There is no guarantee that Arteta departure will bring success to Arsenal. And if it's about success, I admit Arteta will be successful with another team. But are you sure Arsenal will be successful after Arteta leaves the team?
We can see how long it took Guardiola to succeed with Man City in the UCL and this can be a simple example that Arteta currently seems to have failed to bring Arsenal a trophy. But in the coming season or this season, we don't know what will happen.
Even though I don't like Arsenal, the opinion about his departure is not something wise.
There is definitely no reason to believe that if Arteta leaves, Arsenal somehow starts to win some games, in fact, I believe Arteta is one of the main reasons why they did so good and all those players look great on paper because he made them look good, which is why I believe we are not going to end up with seeing him leave.
However, at the same time since they are getting bad results at the moment, we need to remember that he is not going to end up with anything big neither, he can't really end up requesting a lot during January transfer window can he?
I mean if he is not doing that great then he can't make that much money neither, he just has to realize that it's not going to end up with anything beneficial for him. So he just needs to realize, yes he will keep his job unless they lose all their games, as long as they are in top four then he will keep his job, but he will also not be given unlimited money, he is not winning so he is not deserving getting expensive players neither.
Maybe a few small calibre players, like for bench, like maybe 10-20 million range, but that's it and nothing more because with the kind of results he is getting, spending a ton of money because he said so would be wrong.