"Releasing" Onwenu would never happen this year. There's no point. His cap number is $21M. That's made up of $7.5M signing bonus proration that's already paid and will hit our cap this year no matter what, $12M of fully guaranteed salary, $500K of offseason workout bonuses that he's probably going to earn by showing up, and $1M in per game roster bonuses. If you cut him (after he shows up for the workouts) you have to pay him all of that except the per game roster bonuses. You'd take on a dead money charge for the $12M salary, $7.5M bonus amortization and, if before June 1st also next year's $7.5M bonus amortization for a net cap loss of $6M. After June 1st, next year's amortization is deferred until next year so you save $1.5M, net. But same amount of dead money either way.
What's a more practical discussion would be, something like the team converting $6M of his guaranteed salary to signing bonus to facilitate a post June 1st trade to another team. The cap implications for us of that trade would be:
Dead money of $11M this year - $7.5M from his old signing bonus amortization and $3M from the conversion to bonus of half this year's salary, assuming he earns his $500K workout bonus too. Compared to a current cap number of $21M, that's net savings of $10M.
Dead money of $10.5M again next year for the same components minus the workout bonus. Cap hit right now projects to be $25M so savings of $15M.
For his new team, they'd be getting him on essentially a 1 year deal for $6M with per game roster bonuses up to $7M. That's a fair price for someone who needs OL help. Next year's $16M salary is fully non guaranteed so he'd be a cut candidate for them, just a 1 year rental really.
If Onwenu seems like an iffy character guy and multiple young interior OL step up, I could see them exploring a trade like this to save some money on the deal and recoup a minor asset. It probably has to mean Wallace shows well in RG time and both Robinson/Sow look decent enough too.