Remember that this is the second time Riccitiello has bought Bioware and Pandemic. The first time was as a partner in Elevation Partners, the private equity firm that has owned the studios for the past two years. I don't remember seeing an exedus when Elevation bought them. A big part of the reason is that PE folks are very wary of key employees jumping ship and taking the value they just bought with them, so they give them $$ incentives to stay. The same will stay true here; employees won't be cashing out. The deal includes $155M of equity in EA to go to the acquired company, which is most likely earmarked for employee incentives.
Also, to respond to the initial post, if people were surprised by this move, they haven't been paying attention. When Riccitiello left Elevation to re-join EA, it was only a matter of time until EA bought these studios. Private equity shops don't buy companies to hold onto them for the long haul; they either cobble together critical mass, or sell out. And given Riccitiello's affiliation, did anyone see his old partners selling to anyone else?