once u download deltarune, your undertale gamestate is automatically set to genocide so you can't get the pacifist ending anymore, warning on that front
Toby Fox confirmed in a tweet that there will indeed only be one ending to Deltarune, no matter what you do - so the gamestate really does not matter in this case.
Also, he confirmed that apart from Ch. 1 he hasn't really worked on the game, so we might be waiting another couple of years, sadly enough.
Edit: This is NOT Undertale 2. It's a completely different story with some re-ocurring characters.. as he has explained in this tweet.
https://t.co/0k17es53Vr?amp=1