Even Satoshi left the forum a long time ago and up till now the forum still continue with more new active members, so if the forum can survive this long without its creator, it will continue to survive regardless of who left or stay. People find things that interest them daily and if a user left the forum and suddenly the account becomes inactive it may not mean that they left forever, some just gave a break and in the future, there is the possibility of them returning unless some members like Lauda who made it clear that the account will never be active again but since the forum does not have self destroy feature one can not really tell of the account have exited the forum finally or just on a break from the forum.