OP, I'll be straight forward with you.
If this veteran player really IS chasing away players with his attitude (especially as many as you claim), then in accordance with your story f your GM, I would branch off from that guild and create your own or find a new guild. There are implications I can see in the future happening to that guild. For starters, The lack of a GM presence will only make this situation worse. Also, if he's chasing away that many players, then by now most likely your guild has a terrible reputation with PuGs since word travels remarkably quickly. Anyone would agree with me when I say this: Once you lose the PuG community, that guild will be destined to fall eventually.
I was in a similar situation like that in my earlier days; the GM and a few officers were assholes that were EXTREMELY conceited. In a blind fit of rage, he kicked everyone I invited to his guild (we joined from another guild due the that other guild being casual...we wanted to raid). When the day was done, only five people were left in his guild (Him and his officer friends), and they never really managed to recuperate because everyone had already blacklisted the shit out of their guild. We went unto to form out own thriving guild, while that guild leader gave up on WoW and went unto SWTOR.