2) Shohei Ohtani leaving in free agency
You might be surprised to not see Ohtani departing as the number one fear for Angels fans, but Angels fans already see this coming. No, they're not happy with that, but it's the likely outcome.
The bottom line here is Ohtani has very little incentive to stay. The money will be there regardless of where he goes, and the Angels don't give him the same chance to win as other teams that will bid similar or even larger sums of money do.
Ohtani departing for just a draft pick is obviously the worst case scenario. This Angels team won 73 games with him putting together maybe the best season in Angels franchise history. Losing that and somehow improving would be a tough sell. Sure, injury luck could be better and young players could improve, but Ohtani just won the MVP unanimously. He's impossible to replace.
There's always the chance Ohtani chooses the Angels unexpectedly valuing comfort over winning, but that's a tougher sell. In all likelihood, Angels fans will see one of their worst fears coming to fruition which is, well, frightening.