The few things that will, might and never happen are:
Giving birth- Belle
Couples saying I love you- Zelena to Hades (Probably, but we obviously seem to know that we may never Hades again after that).
Wedding- Not gonna happen! Because we were already announced there will be no wedding this season.
Couple’s reuniting- Most likely RumBelle because they have a habit of splitting up and getting back together every season.
Fatalities- Possibly Robin (but not completely clear, since the filming is out of order, but don’t count Roland and Merry Men leaving because that Robin is clearly dead, cause they might come back if they find Robin is alive). Perhaps more then one. Killian (Possibly, because we were hinted that Emma has to learn to move on and let go)?
Break ups- RumBelle (unlikely)?
Leaving town (For good or temporarily?)- Most of the main cast according to spoilers but they return to Storybrooke.
Resurections- Technically Hook because he was dead but is being brought back to life (but it may not stay that way forever).
Engagement- CS (doubtful). Cause engagements would involve weddings and rings. And we already know there is no wedding and no ring was seen or mentioned in BTS. The BTS photos don’t actually mean or refer to an engagement, because fans are imagining that are not true all the time.
Timewarp- For what?