I've read many articles over the last 20+ years saying why we shouldn't rely on ISP-supplied email addresses. We moved to webmail for our main email accounts in the late 1990s and only used ISP email for a small number of NZ businesses and websites. It's always been a worthwhile move because we've had access to newer email features and better options when travelling. Switching to webmail would have been worthwhile even if we'd never moved away from the ISP which has gone through several names: Paradise/Clear/TelstraClear/Vodafone.
I think that most of us have been "fortunate" that we have been able to hold onto old email addresses (e.g. @paradise.net.nz) so long after the brands and companies have disappeared. Except that we are now paying the price of thinking we would have ISP email forever. Around the world, many people have learnt that this isn't the case. We could have been as badly off as many user of ISP-supplied email in the USA who have had to change every time there is a merger/takeover:
http://www.jolanders.com/website/zzz_email_and_spam_reduction_tips/website_email_address.php
how many people had email addresses @mediaone.net? Then in February, 2002 Media One became AT&T, and all of a sudden everybody's address changed to @attbi.com. People didn't get a choice; they had to notify every mailing list, business associate and friend about the address change if they wanted to continue receiving email from them. This happened AGAIN, in July of 2003, when all the @attbi.com addresses were changed to @comcast.net, and all those people had to notify everybody a second time.
Those few accounts that depended on Vodafone were switched up to a year before the service closed. That seemed an obvious thing to do so we had lots of time to handle forgotten accounts that produced an annual email. If we didn't remember the account and didn't receive any email from them in a whole year then we didn't really need them.

