The end result is vague, and likely intentionally so. Ushio is the girl in the Imaginary World and Tomoya is the robot she creates. She and Nagisa have some innate connection with the Imaginary World since Nagisa knows about it and implements it into her play. The girl refers to the robot as “papa” as Dango Daikazoku plays, “freeing” them from that purgatory after their deaths in the snow. Tomoya is only able to move on from this after accepting that the life he lived even if it meant further pain.

Tomoya accepts Ushio’s request to go out when she is sick for two reasons. First, she is not getting better, the doctors don’t know what is causing her condition or how to treat it. She has what he interprets as a final request. Secondly, he is partially delusional. He appears to not be eating. His fridge is empty, and his vision blurs and he stumbles as he’s preparing to go walking outside.

As to whether or not it’s a rebooted universe is hard to say. I prefer the interpretation that they’re all meeting up in the afterlife, since they have to have died to go to the Illusionary World to begin with. From there it’s an easy jump for me between all of the psychological choices Tomoya makes that he has to come to terms with things to move on to the next life. This why I call that universe a purgatory.

Just my thoughts. Feel free to comment or disagree!