As I noted before, that's not the case for every team. Teams with top QBs, to turn around a metaphor, "will allow their ship to go down with their Captain"
If we go 0-2 and Goff is looking terrible with 4+ INTs per game, then don't expect him to keep starting especially if Mannion's looks good in the preseason.
The takeaway is only that Goff isn't untouchable and while he has the pole position and the team will give him every chance to win, if he falters (which again, I don't expect in the slightest) then he will be pulled.
Goff won't get "quite a few games". He's never done anything to earn that latitude.
I expect him to be successful. And, no, he's not walking a tightrope where a few bad plays put him on the bench. It's just that he's not going to have a leash like Brady, Big Ben or Ryan would.