User blog comment:EmrysOfAlbion/Gauis/@comment-4879894-20120505093137/@comment-4623180-20120505100138

That knowledge should have passed onto Merlin, by now. I mean, the episode Lamia.. one thing it was actually good for- we saw that Gaius trusted Merlin to carry on some of his work. It's been several years now, I think that if Morgana can find out what she wants and how she wants, Merlin can. Merlin is destined to be Arthur's magical advisor, and Gaius is meant to be an advisor is he not, so it may be time for Merlin to replace him.

Perhaps when Gaius dies he can leave his knowledge behind in some form? Not exactly like Obi-Wan did with Luke Skywalker, he was a voice inside his head, but close.