When you say 'finish the job he started here' what do you mean? When is a managers job ever finished? How much further could he take us if he stayed? If I am honest, I think he has restored Norwich to our rightful place. A side capable of mid-table prem finishes but with the constant worry about relegation if things dont go well with any championship seasons to come having us finishing in the top 6 consistantly and challenging to get back up. In the real world that is where we are as a club. Poor management over a number of years saw us fall from that and Lambert as restored it. Occasionally we may do really well and get a little further up the league or get a decent cup run.
Sadly, the playing field is no longer level enough for us to be looking at the 92-93 season as where this club could be. Maybe one day a mega rich benifactor might change that (like Man City, Blackburn (briefly), Chelsea etc) but until then we are what we are. Some would say that the job is already finished....
I'd agree we're back at around our 'natural level' (and what an astonishing achievement that is), but I think there really is the possibility of raising the bottom end of that scale.
I think we are genuinely capable of being a solid mid-table side and if that becomes our base, the posibility of what we can achieve rises (though obviously still limited).
Despite the success we've had these last few seasons, that mid-table establishment remains a long term goal and whether that can come fast enough for Lambert remains to be seen.

- though I did put a disclaimer to say please merge if duplicated.