There are tons of reports of npcs not being visible in Legion Dalaran since TWW went live.
After completing the Harbinger portion of the TWW intro, I opted to take the skip from Thrall in Silithus for my lvl 70 shadow priest (the third character I have taken into TWW zones), I could see quest markers for Warmage Silva in Legion Dalaran, but he was still phased out.
I thought interacting with Brann Bronzebeard and the zone-selection map (where the skip places you) would be sufficient to get Warmage Silva back, but nope.
Only after flying to the location of the ruins of Dalaran on Isle of Dorn, east of Dhar Oztan and fair distance west of Dornogal, and doing the quest chain that starts there with Thrall and Jaina, and then completing the quest chain through to Councilward Merrix in Dornogal was I finally able to see Warmage Silva again in Legion Dalaran.