Edit - also not sure if it's Tama, but tagging as such for now since her design is very much like how he's drawn her before. And us the other girl a rhino girl?
Wow. I can't lie, I nearly shed a tear. Welcome back!
If you want to welcome him back, you should do so on his own pixiv page. Even if it's in English, he'll probably get the gist if it's fairly simple, but he's almost certainly not reading Danbooru's comment feed.