Farealmer3 said:
Even if your the Supreme Being?
As far as I can tell, you will always recover, unless recovery is actually impossible. Annihilating effect or Omega effect both seem like possible ways to defeat Transmortality; As I don't think merely rejuvenating will restore their losses. Ergo, drain their HP/HD down to 0, and they would be perma-dead. (since they would regenerate with 0 HP/HD and die again)
The Supreme being, with his Omega Effect would have little trouble wiping out timelords.
However, it might be best to note if this is how these abilities intereact; like a Sidebar or something. As far as I can tell, the following things Trump Transmortality/Cosmic String:
Annihilating [Effect] (and other permanent Entropy effects)
Oblivion (Omnific Ability)
Omega [Effect]
Karmic [Effect] (Slow)
Siphoning [Effect] (Slow, but you can drain their divine status low enough so that they lose transmortality)
Akashic [Effect] (If you have this, you probably can already deal with transmortality)
Things that MIGHT trump Transmortality/Cosmic String:
Astro [Effect] (Can you regenerate from erasure from existance?) (Also, Thelemic Effect notes Cosmic String applies, but this doesn't say either way)
Digestio (Can a consumed foe rejuvenate normally or even at all?)
Transtemporal (Foes without slipstream are slain instantly)
Abrogate (Cancel out their transmortality; Risky, since you are then unable to stop them from using their nastiest power on you)