Sega will join forces with Sammy after all, so the Sega-Namco crossovers will need to wait for now.
In February, Sega's parent company CSK, announced that would go after a merger with Sammy Corp., creators of the Guilty Gear series. A few months later, Namco expressed interest in acquring Sega, and soon set a May 9 deadline seeking Sega's decision.
Sega didn't need that long, though, and a decision has been made: Namco's offer has been turned down, and the original deal with Sammy will go through. The reason for this move is that CSK feels that Sammy is stronger finacially, and that the move would make more sense for Sega, who also has stakes in non-videogame markets, as does Sammy.
While the Sega and Sammy merger still isn't set in stone, it's still likely to happen after three months of talks. E3 may reveal more information about this merger mess, and if it does, we'll have it for you.