I like to think Khadgar earned some time off, after being a major character during both Warlords of Draenor and Legion.
I can imagine him back in Karazhan, in the Library catching up on some old books that Medivh left out for him but he never got around to reading, or enjoying a show in the Opera Hall.
Moroes asking if he’s hungry and maybe bringing him a snack every now and then 
World of Warcraft has a massive cast of characters though, and that does mean people will drift in and out of the spotlight from time to time, even someone like Khadgar.