The more optimistic assumptions that this won't make much of a difference, seem to be based on assumptions that we can hope for, but are far from sure things. The last two years we were in similar situations where we couldn't afford to lose someone else but then we did. If our bigs miss two or three games each over the season, that might be close to normal.
Not missing any is the best case scenario, not the most likely. Another season ending injury probably won't happen but it certainly could. There is lots of time before the season begins, and then a long season before the NCAA tournament.
If all the big candidates stay healthy and meet or exceed expectations we might be fine, but at best we lost a major cushion against further unfortunate events, or players that fall short of our hopes. The odds that Jana will be significantly missed in at least 5 or 6 games or so seems pretty high to me, just because of a normal level of minor injuries, and the consequences even greater if Ice, Ayanna or Amari don't match our hopes for them.