The problem, for me at least, is NOT a question of do you Brock or do you not Brock?. You have to pay Brock. The real question becomes how much do you pay him, and for how long? If I were the Niners, I'd pay Brock for, say 5 years, or 3 years with an option for year 4. If, within a specified, and agreed upon, time period, the Niners do not make it back to the Super Bowl, you don't renew the contract, and you either let him walk or trade him for assets.
Not many quarterbacks have a long enough career to be able to endure multiple cycles of becoming a contender. And most of them see that second cycle be a much shorter one. I think you have one more solid run left with Brock leading the way. If that don't work out, move on.
And, what I've outlined above is, quite precisely, why I despise Jerruh for giving Dak that stupid contract.