I don't buy this one bit. They're trading one emperor for a more malevolent one when Teach kills WB. This type of thinking severely underestimates how dangerous the government regards the stronger level 6 pirates or any of the level 6 pirates. Even WB took note of buggy's group which is mostly level 2&1 pirates with some 4&5 littering the bunch as a slight potential threat to his men.
Collectively the new Strongest Man in the world and his crew, Catarina, San Juan wolf, Busco Shot, Shiryuu, dozens of level 6 pirates serving as fodder, maybe even more level 1-5 escapees left hanging, and anybody Iva didn't mention might be considered as dangerous as WB, Marco, Jozu, Thatch, and Ace+ 1000+ level 2-5 fodder. Sure Teach will gain even more followers around the world laughing his ass off on the Big Screen when all is said and done. So in the end I highly doubt they'd trust Teach enough to ask him back, fearing him too much and I doubt he'd be interested in helping them either.
Is it ever stated that Teach added the Level Six-ers to his crew? >_>