http://www.gamesindustry.biz/articles/2013-…D100m-to-market
A large team (200'ish), I figure didn't lose that many folks after the original Bioshock so they probably had over 100 for long while, working on Infinite for 6 years, selling 3.4m. And if that article is right about the marketing then that probably doesn't even come close to break even.
Still, it does seem pretty insane that the studio just implodes because Levine isn't hot on doing big scale games anymore. Dissolving a studio of that caliber seems nuts, but yeah it probably was sales combined with Levine wanting to step down.