Yeah, they fucked up. Sounds like they're not handling it well, AND there is no fucking way I'd ride on a chain that's missing an o-ring. They should be handling it today. Sounds like the tech manhandled the chain, ripped the o-ring, and is now trying to cover for it. They should have had you ride it back, pulled the old masterlink, and installed a new one. It takes all of 10 minutes to do the job if you're not a moron or it's not your first time. I'm not a dealership tech, missing some of the tools that would make it easier, and installing one with a c-clamp, vice grips, and a punch would only take me 5 minutes.
Everyone makes mistakes but they're doing a shit job of handling this. Not to mention that riding around with no grease in the chain (because there's nothing to keep it in now that the oring is gone) is going to cause some serious wear on that link of the chain. I wouldn't want that on a brand new chain. Nothing they've done so far is acceptable, IMO.
In fairness, I have very high standards for my motorcycle, but I also have an aversion to replacing the cases on my motorcycle because someone can't be bothered to install a master link correctly.