Especially if they're not planning on defending anytime soon, or possibly never. After he fights Nate, if he asks for any fight other a 145 lb title defense, he should vacate. Frankie rightly deserves a crack at the belt, and Aldo deserves a chance to reclaim it. Especially considering how he lost it.
These guys shouldn't be denied because of the "champ's" pipe dream. If he does hold the belt and fights RDA or Robbie, I don't think he should be considered a 2 division champ if he wins one of their belts then vacates FW without a defense. Technically, he wouldn't even have been in the division for two fights and if he doesn't go back, I don't think it should count. But I fully expect the UFC would call it legit and give him the record.