When it was announced he'd been fired, I figured something like this was coming because pretty much the entire cast and much of the production crew are people who really, really, really like James Gunn as a person and really, really, really like working with him.
The jokes were pretty tasteless, of course, but, let's be honest, can any of us really say we haven't laughed at tasteless jokes? To this day, I can watch old clips on YouTube of Richard Pryor and George Carlin telling some of the most tasteless, offensive and racial slur tinged jokes in the history of stand up and I literally laughed so hard a few weeks ago that I even pissed myself a little. To some degree, Political Correctness is becoming a parody of itself when you have someone who, for whatever reason, sat through a decade worth of Tweets from James Gunn for the purpose of seeing if they could find anything bad, or something that would offend somebody as that's the easiest thing in the world to do these days, so that a big case could be made about it and it was a resounding success.
As to Batista's threats to quit, I think Batista is way, way, way overestimating his star power. Drax the Destroyer isn't exactly the deepest and most eloquent character just as Batista isn't exactly the most eloquent and well rounded actor. Finding a replacement for him wouldn't exactly be like searching for the Holy Grail as, outside of Guardians, he's mostly been in minor, secondary character roles that've been highly forgettable.