I think Rafa has proved, so far, that his big money buys are usually spot-on but he has also proved that most of his cheaper 'gambles' are just not good enough for the Premiership - never-mind a team going for the title. With this in mind I'm sticking with him until hopefully, one day soon, we get owners with more cash for him to take less risks with.
Obviously, this might never happen but as others have pointed out getting rid now could possibly set us back years in terms of rebuilding, so lets see where we finish this season.
If we we got mega rich and he still didn't challenge I'd give up on him to.