The same (semi)recently happened with Willard in the newer Marvel series. It could actually be that Lucas was saving them, considering Rieekan pretty explicitly dies in the original scripts. I don’t recall the name showing up during the development of ROTJ, though…
Since Lucas toyed with having an attack on Yavin being a part of ESB’s story, it’s possible the idea of the Rebels suffering some major losses (ala the Hope Dies story arc) was in his mind at a certain point. I have a feeling some of the higher-ups from Star Wars being dispatched in the meantime might have been something Lucasfilm allowed at the time as a way to fill in blanks once the characters went nowhere. I have a feeling Veers would have shown up if the Marvel adaptation hadn’t labored under the assumption of him being dead (even though he showed up in ROTJ’s early drafts- that would have been fun to explain).