#2 - Oct. 27, 2009, 1:06 a.m.
The e-mail address originally registered to your World of Warcraft account will not hinder the Battle.net merge. You can just create your Battle.net account with your current e-mail address (not an old or defunct one) then merge your World of Warcraft account on to the Battle.net account. This will update the registered e-mail and the merge will be complete :)
This makes the process easy as you do not need to remember the old e-mail on your World of Warcraft account. As long as you have access to the account itself you will be able to merge and keep playing!