As a free agent? If he opts out of a one year $19.35mill, it won't be to accept a one year $17mill. Maybe a 2 year $34mill. I could see that.
I haven't seen anyone mention this, but one reason he might not opt out is that if he does, the Sox might extend a Qualifying Offer (should they still exist), which will make him a less attractive free agent. If that happens, opting out might position him to take the one year offer for less than his current guarantee. Now, if he was a 27yo Bryce Harper hitting the market, no one cares about the QO. But for a 37yo DH? It's very possible some teams do...