How EF code first modeling will affect already existing data in database

Question

Its clear to me that I can customize the behavior of syncing models and DB schema process. I am using the DropCreateDatabaseIfModelChanges<> class to do so.

Assume that I have a working project and site and DB is filling in the data. Everything is working fine.

One day I decide that some functionality needs to be changed. The changes will affect the properties of my models (they can be renamed/deleted/added, some models will be new, some models are deleted).

My question: What will happen with the already existing data on my deployed site when I check in all of my changes?

Will I lose it? If so, how can I avoid that?