Although it's well-accepted in Seahawk fandom that Earl Thomas is the most critical defensive piece on the team, it's not universally understood that Sherman is very nearly as critical. I think most people get it, but there are some holdouts.

Although oft-repeated, it's not actually true that just being tall is enough for our system. Sherman is something special, it just took Carroll's unconventionality to give him a chance in this league, same as Russell Wilson[1]. In the year and a half before Sherman was starting, our defensive passer rating averaged ~90 per game. As soon as Sherman began starting it dropped to ~70 and has remained there ever since. Passing defense wins championships. That's why the best corners get paid the way they do.
Winning teams keep their All-Pros. Sherman wants to be here. Seattle wants him here. The chances we don't re-sign him are small and if he's the highest paid corner, it will be nominally only and not the most expensive contract by risk.
We'll lose a lot of players. By and large, most fans understand this and I don't expect there to be nearly the wailing and gnashing of teeth that some foresee. Not unless it's one of our All-Pro caliber players. Of course, fans have their favorites, so there will always be a demographic with complaints, but that doesn't mean most of us don't understand how the salary cap works.
[1] Do you realize, Russell Wilson could have easily never happened? Anywhere. What if he went to be Cam Newton's back-up? Maybe Cam gets hurt for 3 or 4 games and Wilson has a shaky few stats like the beginning of his rookie season, maybe even worse because the team is built to enable to a tall QB? Short QBs don't get the leash that tall ones do. Does he ever get another chance to start?