I feel that the current "Ye have everything ye need for yer quest" response when the PC is ready to leave the Drakalor Chain after closing the gate is insufficient.
It's the same thing he says when you get the trident from him but have not yet dived to D:50.
I understand he says this in anticipation of the PC becoming the Avatar of order/balance, and considering that there is no further gameplay after achieving that, he doesn't really need to say anything.
In my case however, I have crowned early, before I even thought about Gaaby's quests and only later decided it would be nice to obtain the trident since I still had that option.
Khelavaster's response after chatting to him once I closed the gate was lacking.
It could be either a praise for completing the quest or admission that the PC has omitted some sort of even larger greatness, to hint at what could have been.
This could apply both for characters that have closed the gate and recovered Trident of the Red Rooster, or just gate closers without the trident, since it's impossible to return to D:50 once the gate is closed.