Hi Bryan, Not sure if this makes you feel any better but you are not alone in trying to make this decision. there is no one right answer for everyone. We don't know how soon EAB may arrive but we do feel very confident it is not a matter of if but a matter of when it arrives. My guess is within 5-10 years. All it takes is somone bringing in infested ash firewood. Here is a really nice website on EAB that may help.
http://www.emeraldashborer.info/ I would recommend seriously thinking about planting replacement trees now. Depending on the location that may be tough to do without removing your exisiting ash. You may want to remove one now to spread out the expense or just wait and see, get a few more years out of them and some added growth on the replacement trees and then remove as they become infested. unfortunately EAB attacks healthy trees and none seem to show resistance. good that you are thinking about it now. Sandy