Part of the problem for those pursuing vengeance is that the Seraphim have been scattered the to winds remarkably quickly and broadly, and it's hard to do anything with so many targets and so few resources. They were the elite of CATCo's security personnel. If there are approximately 2,500 Navy SEALs active today, then I'd say that's a fair guess at the number of Seraphim at their peak.
Some (many, most? No one knows for sure) died back when Ares decided to take over CATCo. Others joined Ares. Some joined sides with the Aurelius clan. Some were recruited by other spy shops, including Jonathan Blake/Centurion Security. The Fallen went off to retaliate, either directly or via the 47 Ronin model. Some just wandered off into the aether. Given Cross's and the Seraphim's relationships with Dunkelzahn and the Draco Foundation, that may continue to be a factor even while some are actively going after the heads of Ares, which would include Nadja Daviar. Some went after Hestaby, believing that she was responsible for the windfall that allowed Arthur Vogel to purchase Leonard Aurelius's shares of Ares back in 2060. And finally, some went off to freelance or just retired rather than to take new masters or go off into bloody clandestine acts of revenge.