It's more of a theoretical ending since they never saw fit to provide Satsuki fans like myself with an ending that didn't include her untimely death or complete estrangement from the storyline T_T. However, much to my enjoyment, Yumizuka is alive and well during the events of Melty Blood, and was even hinted at in the dialogue between Sion and Shiki before she became a playable character in ReACT. I would guess that if you want to pick a canonical ending, it's most likely that it takes place either after Ciel or Arcueid's Good End, as Shiki never encounters Satsuki for more than a few minutes throughout their entire arc, and she just simply disappears from the story with little notice. However, it seems like Shiki knows her much better than in the arcs I mentioned, so it would be safe to assume that she either met him similar to the way she did in the Far Side arcs, just far later after the original story was already over, or that in this storyline, he met her exactly the same way as in the Far Side arcs, but didn't kill her (way to go, Shiki! ^^).
I would have to say that Ciel's Good end would be the closest match for the way all the characters are interacting, as the cast more or less gets along with oneanother quite well.
"They marched onwards, fire against earth, bodies piling ever higher for the whims of rival demons, content in their game. The masses never questioned their intent nor knew their masters, serving Hell more than Heaven in their madness. For madness went unchallenged here, and the great machine of many faces, skins, and thoughts continued to turn in silence."