Release
No one should hold their breath as far as Williams reuniting with Woods. One thing Woody has done "better than most" over the years has been holding longstanding grudges, and Williams didn't just burn that bridge... he stole a page from Eastwood's "The Good, the Bad, and the Ugly" and dynamited the bridge to smithereens.
As far as Greller's babysitting services... he wouldn't take the pay cut. Greller earns almost as much per year with Spieth as the average tour player earns in total who's hovering around the 120-125 mark on the season money list.
I don't know what kind of arrangement LaCava has with Woods, but it has to be fairly lucrative and based above and beyond a percentage of Woods' earnings, considering Woods is still well outside the top-250 in the OWGR and hasn't made a weekend cut in an official event since the Masters back in 2015.
It's not like Woods has a plethora of caddies lined up at his door wanting the opportunity these days.