Thuney is a great player, no doubt. But the Pats have moved on from better players over the years in order to to stay cap competitive. Trading Joe would instantly move the Pats from 1 MM under the cap to over 15MM. Enough to pay for t he draft and add some help during the next wave of FA.
A lot of what the OL will be, IMHO, will depend on how well David Andrews comes back from his lung clots. If he is back 100% then the Pats have one of the better OC's and filling Thuney's slot will be a lot easier than without him. Frodholt and Elumenaur are 2 possibilities, but additions from the draft, FA or trade are other possibilities.
In the end, there will be a lot of new players still to come here over the next few months. about a dozen or so will arrive next week with more to come over the next 3 months.
BTW- if the Dolphins offered me the 39th pick for Thuney, I'd do it in a nano second. Joe Thuney was an all pro last season. But name me a OG the Pats had during a superbowl winning season that was an all Pro. Mankins was the best of the lot, I think, but he never got a ring. In fact it wasn't until the Pats traded him, did they end their "drought" in 2014. Though that was more of a coincidence than a factor. Logan had 2 very solid years with the Bucs before retiring back to the ranch.
BOTTOM LINE - You canbot keep everyone in the cap era. And there are some years where you can't seem to keep ANYONE. This is one of those years. Let's bite the bullet and get our 2nd round pick and move on.