Classic Battle.net Account Expiration

Inactive classic Battle.net accounts are deleted at regular intervals. If you create a new account, you must log in to Battle.net for a total of 2 hours within the first 48 hours after it's created. After that, your account will remain active as long as you continue to log in to it once every 90 days.

Once an account expires, it is permanently deleted. Anyone can create a new account using the expired account's name. Names that have expired and been removed or reused cannot be recovered.

Multiplayer Diablo II Character Expiration

Multiplayer Diablo II characters expire if they are inactive for too long. Expired characters cannot be recovered. Single Player characters do not expire.

Newly created characters will expire after 10 days of inactivity. Characters played for two hours or more will expire after 90 days of inactivity. To reset the inactivity timer on a character, log in to an active game with that character and buy or sell an item, or kill a monster.