Does anyone knows when will HNiles return?

His banner is still running for more than a week, so you still have time.

After that...probably several legendary banners from now.

about half a year from now on a legendary banner. if you don't pull on that you'll have to wait a whole year. if I were you I would try for him while there is a chance now. its not really safe to snipe on legendary banners

I'm still trying to get him now (though given my luck so far, I'm not hopeful). You'll almost certainly get chances at Legendary units before you'll get another chance at him, so I'm not sure I'd save orbs for that while I still have time to try for a seasonal.