Hi Apocalypse,
Given that there's two automatic demotions (8th in each conference) and three qualifier demotions (5 vs 7, 7 vs 5, 6 vs 6) from ABBL, that makes 5 teams that get demoted each season.
Given there's only four D2 winners, I'm almost certain that the highest placing finisher that doesn't win the title also gets promoted.
However, from memory, being promoted this way means you miss out on an attendance boost next season, as well as of course the prize money, so definitely best to still aim to win the league title.