After Roland and Money, we had Black. Black was doing okay but then we brought in the Legend Archie Knox as his number 2 (former asst to Alex Ferguson at Aberdeen and Man Utd who had then done several years as asst at Rangers at a time that they won everything going). I remember thinking what a coup it was to get him and it proved to be when Black's side started performing better than it's players would have suggested was possible. It was Knox not Black that made that squad work IMHO and as soon as we got Reid in and Knox went, the rest is history.
Anyway, the point is, the Asst Mgr role is just as important as the manager - particularly if the Manager is relatively young / inexperienced. A man like Knox, whose CV and history could not be argued with, is someone who young players would look up to, listen to and respect, even if the Manager was new/untried.
Having an unknown or friend as a asst will do no favours and SP would be wise to seek a massively experienced replacement.