1. Two people with whom he developed pretty close relationships are members, and he was shown in SB to at least be thinking about them, even if he was probably mainly motivated by tracking down Nidhogg's eyes. I forget the precise line, but when he destroys the canon he mentions the WoL by 'name' ('aibou', or partner, which is the epithet he uses to address the PC in voiced scenes).
2. He really shouldn't go back to Ishgard anytime soon; he attacked VERY publicly and there's likely to be a lot of resentment towards him for that. I'm sure Aymeric and the WoL would do their level best to make sure people knew he wasn't in control of himself at the time, and it wasn't his fault, but chances are it just isn't safe for him there right now.
3. The Scions need an Ishgardian representative. Every other major power, including Garlemald, has at least one person in the Scions to represent it. Even if the reps for the three original city-states were technically Sharlyans who happened to be working out of those areas (which also brings up the point of whether or not they're going to introduce someone to take over the Gridanian slot).