He kept us up and has certainly got some existing players playing better. Whether any halfway competent manager could have done the same after Robinson's complete dereliction of duty last season is something we will never know. Personally, I think it's certainly possible (he didn't exactly suddenly turn us into world beaters).
Neither do we know how much the good recruitment over the summer was due to him - but you'd have to think at least some of it.
What we do know is that he has done half a job. The strike force is in severe need of bolstering in January, we are light on the right hand side (and possibly overloaded on the left when Browne and Edwards are back) and the current three at the back formation looks creaky. I am pretty amazed that Bristol Rovers have (apparently) taken a punt on him, looking at his record. It seems like the managerial equivalent of signing Deane Smalley because he had one good half season (and we know how that worked out!).
If he stays, then fine - he can try to finish what he started. If he leaves, and especially if he takes his coaching staff with him, he will have got us to a certain level only to endanger all of that progress.