Will my account on d2jsp expire if I don’t log in after a long time? If so when will it expire?

Accounts on d2jsp will not be deleted. No matter how long you are not logging in, the account will still be available when you come back

As derAmigo said, they will never expire. You may need to do a password reset though upon return if you don't remember it.

No, but if you forget your passwords you may not get it back.