He's older than Dre'Mont, so he'll likely command less, maybe 13-15M/yr.
And I wouldn't overanalyze the cap situation this early—future years provide too much flexibility to make reasonable projections. They could bring almost everyone back next season and extend Williams if they were willing to sacrifice some future cap flexibility.
You're right in many ways.
But good generalities can be observed towards next year's cap situation even this early. Last year at this time it appeared that we had plenty of cap for this year - $60M plus if I remember correctly. Most were excited that we'd be able to afford multiple top-tier free agents.
But any analysis showed it was a mirage. We ended up with a $17M/yr IDL who was overpaid and is not performing at a high level (which is what many expected would happen). In addition, we filled holes with a bunch of $1-5M guys.
And then the cap was gone. We had to move what salary we could to the future just to get enough cap for rookie and mid-season emergency signings.
The cap situation is even worse for 2024. Yes, there is money to be moved to 2025 and beyond but, most likely,,not enough to make even 1 top-tier free agent signing. Unless we cut all 4 of the players mentioned earlier.
tldr; I don't think Williams will be re-signed. 2 draft picks for a 10 game rental was not a wise move, imo.