Pu definitely isn't currently allowing Mark to do anything. At least not intentionally. They MAY have had an agreement of some sort back 4 years ago when SAC was still building rockets for AV123, but AV123 hasn't had any affiliation with Onix since at least 2008. I don't know exactly when they split as AV123 was likely selling the rest of the Ref 1's they had in stock for a while after.
AV123 stopped putting the Onix name on the Rocket boxes at some point, and removed it from the X-series stuff a bit before that, but any continuing use of the Onix name is not ok. Certainly I understand it's not the fault of any owners of older gear that the branding is inconsistent, and it's going to be a long uphill battle to re-establish the Onix name as a separate entity, but I wanted to make it clear that that there are definitely not any ongoing agreements, and Onix has always been a completely separate company.
That said, I can understand your concern about replacement parts and such. I would assume that AV123 get's the drivers direct from the manufacturer. The vifa xt25 tweeters are easy to find, but the woofers aren't off the shelf. I think they may also built by peerless though. (feel free to correct me if I'm wrong) Ultimately, they will be available as long as somebody is willing to pony up for the required quantity. I have no idea whether that would continue to happen if AV123 folds. As far as an upgrade path, I'm afraid there's not a clear one. There is no similar line above the rockets, and no company will "inherit" you as a customer, unless somebody buys out AV123's designs at some point. (not a terrible idea if the price is right)