Hey, Orchid will be fine! Even if he falls off the ramparts, he still has Relentless Endurance to survive to 1 HP.

Though admittedly with how death saves work, I don't know how high he has to fall before the damage done to him will be considered "Instant Death". 

Also a quick question [@Hekazu], I'm perfectly aware that the dragon is huge size and I know that Orchid can't technically grapple it (I think it's only medium size or smaller). But could he still make a grapple attempt to simply hold onto the dragon, instead of trying to hold it in place? I imagined there being some sort of aerial face stabbing action going on later into this fight, and Orchid is going to really need that bless and rage ASAP. Oh, and Fairy Fire. That would be helpful for Orchid.