If you promote SERVER1 installed as a BDC to be a PDC, then the old PDC (SERVER2) is automatically demoted to BDC status. If you don't like SERVER1 being the PDC, just promote SERVER2 (from BDC to PDC) again. It's not that complicated. It's simpler than it would be in a Windows 2000 domain, when there are subtle differences between the roles that difference DC's take.
Once a system is a BDC, if you want to eliminate it, you can just take it off the network and reformat it. You should also use ServerManager to make sure that that server is no longer listed in the list of servers, otherwise you may occasionally see errors about syncing.
No worries, I've done this dozens of times.
ShackDaddy