Help:Archiving
Talk pages should never be blanked, nor have any comments removed (this includes the welcome), by the user whose page it is, nor by anyone else.
Instead of deleting any and all information on talk pages, they should be archived by an administrator (or in the case of a user talk page, the user) where they can be accessed by anyone. When archiving, the entire page must be archived by moving the page as to keep the edit history intact.
An ideal location to move your talk page to is User:Username/Archive Number. So, if User:Example wanted to make his first archive, he would move his talk page to User talk:Example/Archive 1. His second archive would be at User talk:Example/Archive 2, and so on. Other variations on this somewhat bland naming style are allowed, for example: User talk:Example/First archive, or User talk:Example/Archive 2008-2009.