Background: I have some existing apps in the App Store and I have just renewed my Apple Developer Program membership.
Appreciate if someone can help with these questions:
1. No, your apps are there to stay on the app store. Distribution profiles do not expire until you force them to. Even then, the expiration only keeps you from submitting new apps with that certificate. It does not effect pre-existing applications.
2. Nope! Jeez, that'd suck...
3. Yes. Apple actually applies their own certificate to your app once it is submitted. Your distribution certificate only goes as far as Apple's verification process.
You're good friend. No need to freak out. The provisioning/signing/profile process is a pain in the a**, but fortunately for us we don't have to worry about things like this.