If Williams has a really good year, he'll command around $17mil per year. Or, about $70mil for 4 years, likely half of that fully guaranteed. Might the Rams do some cap antics to try and keep him? Maybe. But I doubt it. I suspect they'll be looking first and foremost at LT. If a really good vet LT comes available, they'll make a big play for him.
The thing is this: if he has a so-so year, he'll still command a big number. But no way the Rams would pay $11 or $12mil per year for a guy that is reasonably replaceable. Not with Ramsey manning the other side.
Bottom line: they are well more likely to keep him if he has a really good year than if he has just an OK year.