I shared your see-it-through approach when everyone wanted Parcells gone. My words of caution back then to fans were, "Be careful what you wish for." We got change, and it was the sort of change I always feared.
So I see what you're saying with regards to Garrett. And, yes, he shouldn't be let go if a solid replacement plan is not in place. I'll be the first to admit I don't know who should be the guy. And, no, I don't want him fired only to have Jerry caught with his pants down as he realizes there's no one to hire.
But this offense was inadequate, and a lot of the problems pointed to a poor offensive coordinator. From the play calling itself, to the game plan, to the inability to mix in our various runners, to the unwillingness to stick with a running game, to our inability to understand or react to what opponents were doing. Our team is full of a bunch of softies, so I'm hesitant to take THEIR word that Garrett is failing them, but I do think it's telling that Romo and Owens are so willing to lay it out there in explicit detail just how it is that Garrett has failed this offense.
Maybe keeping Garrett is the answer. Maybe he has a bright future and needs time. But 2008 showed he's not equipped to be the sole mind of this offense. Remember, you credit him for 2007, but he had Sparano right by his side, who, at last check, is doing fairly well in Miami. Perhaps we overvalued Garrett's importance to last year's team and undervalued Sparano's. So, at the least, he needs someone in here to help hold his hand through the process, as silly as it sounds for an offensive coordinator raking in $3 million.