You can still burst her before she can activate it if she doesn't expect the damage.
Do you realize how insane your burst would have to be for a good morgana to not even see it coming? There's only 2 champs I can think of off the top of my head that have enough burst to either kill her instantly. Veigar happens to have a highly telegraphed burst, and Graves is banned, all the time. If this is blind pick, then that's a moot point.
Every other bursty champion has enough burst to burn her zhonyas (Provided they're not ahead by like 5 levels), but not enough to actually kill her.
The only way I can see her living is if nobody is trying to kite backwards and she uses zhonyas and then nobody can break the chain.
Kiting works really well if she didn't have a binding she could use to effectively take one of your teammates from you.