In the Cyber Missions cartoon, which takes place after ROTF, Frenzy is shown to be alive.
This doesn't cause a huge continuity problem since the ROTF prequel 'Veiled Threat' novel shows that Frenzy's severed head in the ROTF movie was actually still alive. It was just being kept as captive by Seymour Simmons and was dormant when it was not activated. It is possible Frenzy somehow escaped at some point and reunited with Barricade.
This doesn't cause a huge continuity problem since the ROTF prequel 'Veiled Threat' novel shows that Frenzy's severed head in the ROTF movie was actually still alive. It was just being kept as captive by Seymour Simmons and was dormant when it was not activated. It is possible Frenzy somehow escaped at some point and reunited with Barricade.