To play devil's advocate, as is my lot in life, apparently, the context of the question was asking about Zasalamel and Abyss based on the ambiguous nature of the games before SoulCalibur V with relation to each other, where between one or a few (or perhaps none, just elements of some here and there) endings are canon to the next game, and this is before we introduced time travel as a concept that can actually occur by the characters themselves. So one possible interpretation of the various what-if scenarios the characters find themselves in in their self-contained game could be that they're on multiple timelines. That wouldn't, I wouldn't think, have any bearing on the new unified one story canon approach. If I were on Twitter, I would follow up this question to ask if that concept holds true in SoulCalibur VI, because this answer by itself is inconclusive as it pertains to our current situation.Well, "there are multiple timelines in Soulcalibur" definitively answers the multiverse question.
I still feel like we're conceptualizing this whole thing differently. With my current choice of timeline model (because we don't know what it is for certain) being the single line (so think Back to the Future), because they've only shown travel back to the past thus far, there are not "two Cassandras", in the meta sense of the word. There is only one Cassandra, and it's the future self of Cassandra that visited her, and so they are one in the same. The act of future Cassandra visiting her past self changed her game plan slightly and convinced her to take an early trip with Sophitia's old weapons, but then she didn't intervene with anything after that. Sophitia and Rothion still got married and are still on track for having Pyrrha and Patroklos.Our current Cassandra couldn't be the same because our previous Cassandra never went on this initial quest. She could certainly end up in the same place as the other Cassandra, but if there is going to be a time loop in play here, it hasn't yet become a stable one where there are no variations from round to round and the people involved are literally the same people, memory for memory, thought for thought, and action for action.
Even if that's where we end up going, though, we'll still be looking at one line of time that ran from "Soul Edge" through SCV and then a separate line of time with its own distinct specifics perpetually looping back on itself. The prior line will never be affected by this, nor contain events like Cassandra's new inaugural expedition, Zasalamel's 1590 epiphany, and whatever specific thoughts and actions stem from these newly introduced variables.
It's quite likely that in SoulCalibur VII, Cassandra will protest Sophitia from going on her quest for SoulCalibur II events and steal Sophitia's new weapons, as happened previously, causing Rothion to have to forge up Sophitia's old weapons to match her new weapons (so that Sophitia can pursue Cassandra) and then begin work on Cassandra's Digamma Sword and Nemea Shield, since she won't be swayed from that point forward from joining the fight. Whether or not Cassandra does anything differently from there remains to be seen, but remains a possibility. If she does do something that changes the future, then her future self that visited her would be erased, and we would move on to a new stage of history. If she does not, or is not able to do something, due to the Astral Chaos getting in her way, for example, then the loop closes and we're right back to where we were, and she'd try again.
But it does indeed appear that everyone else who hasn't had a timeline-specific event (so everyone other than Cassandra and Zasalamel, as far as we know) has no idea what's going on, are the same people, have their same memories, thoughts, and actions. New actions that don't cancel the previous version of the story's actions are not "different" actions, just because we didn't know about them before, to cut that response before it comes, so Setsuka, for example, is not "changed", in the technical sense, because she's still primed to do her SoulCalibur III stuff like she normally did.
Fair enough, like I said it's only one possible thing that could have prevented Sophitia from having to sacrifice herself, but I do feel like Pyrrha especially is going to present a problem in the future, because that's what happened originally to cause Sophitia to be willing to give up her life in the first place. I still would have volunteered to have the children for Sophitia if I were in Cassandra's shoes, just personally. It would have taken some explaining, to be sure, and maybe I'd have been thrown in the nuthouse or not invited to family events anymore, but it would have been worth a shot. I'm not saying prematurely killing off the children would have been my first choice, it's just among the possible selections. I'm mostly still cross with Cassandra for not acting yet.But Cass has no reason to believe that preventing her own sister's children from being born is for the greater good. Saving Sophitia is a desirable goal, and inarguably a good one, but it isn't necessarily the most important one -- certainly not to the extent of treating the children's demise as inherently preferable.