I think you have to stick with Petrie at least the next three years.
First, and most importantly, I have absolutely zero confidence in the Maloofs picking his replacement. I'd bet my house that if Petrie gets fired we get to see the new reality show "Who Wants To Be The Kings GM".
Secondly, this years draft pick, possibly next years draft pick, and our free agent signing(s) whether we get cap space this year or in 2010, are going to determine whether we have a team that can contend or are stuck in the lottery the next 5 years. Petrie has a great record in the draft, although most of it has come from getting value in later picks, and you still have to take his record against an unknown replacement. Same with free agency, he has a terrible habit of spending the MLE every year, but most of the guys he has brought in have both fit well with the team and played at least up to expectations. His only big free agant signing was Vlade, which worked out very well, which has to compare favorably to anything John Whisenant or Jerry Reynolds or whoever else the Maloofs may decide as his replacement have ever done.
I have a lot less confidence in Petrie than I did in 2002, and if Kevin Pritchard was knocking at the door getting rid of Petrie would be a no brainer to me, but there's steep drop from Pritchard down to Kevin Mchale or Isiah Thomas. I think that you give him the next two years to get a team together, and a year to prove if it can succeed. If you don't have a winning team by then, he should be out the door, but his record can stand up with just about anyone out there, and I'd take my chances with that especially considering the magnitude of the decisions the next two years.