I feel like I've been to the parks at points in time when pretty much every attraction I love has been down (obviously different trips).
With that said, the ones that would kill me if they were down are honestly the ones my kid can ride, as I can understand why they need to close these from time to time, but my kid wouldn't get it. So for me:
Small World, Dumbo (and any other variation of this ride), Peter Pan, Philharmagic, The Seas with Nemo, the shows (Nemo, BatB, etc).
I've still enjoyed my trips without hitting a single thrill ride due to my DW having motion sickness pretty bad, so I'm happy as long as I can see my kid happy on her favorites.