This is slightly incorrect.
Massive spoilers ahead, I read raw EN to end.
Something happened causing Tia and Ed to share a soul, or part of a soul, or something to that effect. (I think IIRC her dying as he warped out of the world in 1st lap 2nd visit while making his wish with the ticket?)
So she was partially thrown outside the "loop" of causality, and was able to trace Endroll (the Demon Lord of the End)'s power with the Winged Sword. More like a foreign contaminated body being thrown out/dragged along, rather than "gracefully" allowed to leave.
The god is NOWHERE as kind as you recall. He's a vindictive immature insecure bastard.
Uh.... I don't think this is correct either. Unless you mean something else.
I read WN to end. Tia and Ed DO end up together... for eternity? They just never sleep together on-page. Is that what you meant about "end up together"?
And although there are other women Ed "seduces" -- for lack of a better word -- he can't take them with him. (RIP Edda-chan, the Last Fragment of Possibility. )
I won't spoil the major twists or plot or ending, but although there are arcs without her, Tia is on the final page of WN with Ed.