Had nothing to do with the Impacts.
Vince Russo accidentally emailed the wrong Mike in his address book (Johnson from PWInsider, not Tenay) mentioning stuff for commentary. The only way Russo could have done this is if he was still involved in the company, which the email basically confirmed he was, and which everybody except Spike already knew. Johnson threatened to publish the email, so Russo confessed on his site. Spike's people have Internet, and saw the whole thing. Spike hates Russo, and demanded TNA release him in the first place after they no longer had Hogan/Bischoff to drown his bigotry out. Spike finding out TNA lied to them about getting rid of Russo was the last straw, and days after the news went on PWInsider, they decided not to renew.
Like Meltzer said on LAW overnight, Russo "had everything to do with it."