If policy has changed recently (recently is relative term), it is probably impossible to get the word out to all individuals at all levels, even those that need to know/should know of the change, in a huge company.
Chances are that the email account will be retained past the 60 days; however, it is retained through Yahoo. How much do you trust Yahoo? Think about all the features once offered by Yahoo that have been terminated. Think about the notorious reliability of Yahoo's mail handling!
It will cost a few bucks but I think the easiest thing to do is get your own domain name. Hand that out to your contacts and tell them that it is your permanent new email address. That way you won't have to worry about whether it will work or not once you kill off the dsl line.