ObjectGears

When you are changing the zones the system will not allow you to delete a zone in which webparts are present. If you want to delete a zone than you have to move the webparts into another zone and then change the page design.
Therefore, you cannot lose your existing webparts.

When changing zones the system will not allow you to delete a zone that contains webparts. If you want to delete a zone, then move the webparts first into another zone and then change the page design.
Therefore, you cannot lose existing webparts when doing changes in the page design.