I have a BTInternet address from maybe 15 years back. When I got business grade ADSL it was not possible to transfer it over but required dialling in once every 90 days or so. I did that for a couple of years but then left it. Anyone who had a consumer ADSL could move their address to that account - but not business accounts. I have not dialled in for several years - and have an auto forward in place.
I have just logged in and can send emails from the account and mails are definitely forwarded.
So, there does seem to be some randomness as to whether an account remains or is deleted.
If they do move, ensure they put auto forwarding on - login to UK.mail.yahoo.com and it is under options. There are vacation response and forwarding options.
M H C
taurus excreta cerebrum vincit