Exchange 2010 with existing 2003 Exchange

I had a server acting as DC, AD and Exchange 2003, I introduced an Exchange 2010 and had moved some mailboxes.  All the mail was still passing through the 2003 box, I lost that box today and have not been able to get it back.  Is there a way to make the existing 2010 box work without getting the 2003 box back online?  I have a 2nd DC and backup AD.

Thanks