"I think you recover mentally much faster if you have something to go back home to. So having a job waiting for you will be mentally easier to deal with."
Ditto. I've done three such trips now, and in each case I found it all too easy to slip back into the old ruts. But I have a very established situation --- married over 30 years, a house and just generally a pretty settled and comfortable situation. For so many thru-hikers, they were able to do their trip precisely because they're in a transition of some sort. So by definition their life is unsettled above and beyond the thru-hike.
I think it's pretty tough to separate out that factor from what every thru-hiker goes through just based on general mental/physical issues.
On my last trip in particular, because I spent so much time alone (on the CDT), I found myself somewhat more de-socialized than usual. I was happy with conversational silences which earlier I might have found uncomfortable. I was less comfortable in larger groups or crowds. This has happened before, but it was a bit more intense for a couple or three weeks this last time.
But as Piper suggests, having something specific to go to, something to start doing will likely make the transition easier, so long as you have a little recovery period.
Eating: you just have to try to back off sooner than you might otherwise think --- especially if you're older or otherwise inclined to pile on the pounds easily. I suggest at most a week and preferably somewhat less after you stop hiking before you work on throttling back the calories (and desire).