@mp13: I came across your question while google-searching it myself. From what I can find, they haven't been involved past GL:New Guardians 40 & (pre-rebirth) GL 39, where they told Kyle they were leaving to go do good across the universe, and talked to Hal prior to his leaving the GLC (respectively). Comic Vine's appearance-listing for them has them appearing in more GL issues, but looking over a few I didn't see them (maybe they were mentioned in passing by Hal, but they were not physically in the story).
I imagine they they were essentially forgotten/written off, just so the writers could move on to introducing the guardian with the phantom ring (his name escapes me) & re-introducing Ganthet & Syad. When they recently mentioned they were the only guardians left I thought, "wait...what?? What about the ones who had guarded Volthoom??"