If you get a notification that your instance is going to get terminated - then yes, you can stop/start, but then you will lose ephemeral disks (but not EBS volumes). If you get a notification that your instance is just going to get rebooted, then nothing's going to get lost.

As I said above - the terminology can get hairy pretty fast. It's valuable to take stock of what you really need persisted, and what use can be made of 'scratch disks'. Local ephemerals are fast and cheap (included in the price of any instance). They come with the operational overhead of needing to rsync data off of them yourself if you want to retire that instance however.

No, not ephemeral disks. They're typically used for temp files, caches, etc., or servers you can afford to lose. EBS volumes are persistent and work just fine between stop/starts.