My opinion is that if XXX bought out EDIG, then they could recoup some of their investment by going after the remaining identified infringers, should XXX decide to do so.

I doubt that XXX would want to have the patents declared 'invalid' if XXX was thinking of buying out EDIG. Otherwise, there would be no future potential to request an injunction on the importation, manufacturing, or the sales of other competing (infringing) products similar to XXX's products using the patents, if XXX had the patents found to be invalid.