Sad to even think we might not keep him
That's not even remotely on the table. Don't overreact to a gigantic contract negotiation dragging into the summer. It happens pretty much every single year.
Especially for a locked-in veteran player (and one that's had health issues before) like Bosa, there's no burning need to get him onto the practice field immediately. He can sign in late August and it would be fine.
It would be one thing if Bosa was expressing dissatisfaction with negotiations. He hasn't been.
There are real holdouts, and then there are, "negotiations are going fine, but I'm not risking injury on the practice field until the deal is signed" holdouts.