Restore restores whatever was backed up. Including table, field and index definitions. So if you restore an old backup on top of a database that has had changes made to it's schema you will lose those changes just as you would lose any data changes that had been made to the replaced database.
Restore does not, however, have to restore into the same "physical" structure as the original backup -- you can change the number, size and location of db extents; but not the "logical" structure -- that is all the same storage areas must exist, the rows per block is the same and the db block size cannot be changed with a restore.
As Casper said, if you roll forward ai files after a restore any schema changes that were made to that database since the backup will be applied to the target by the ai roll forward process just as they were on the original.
