On the forum we regularly delete users who have created an account, have never posted anything, and have not logged in for at least a month, but on the actual z/OS system the admins only had an informal policy of deleting users who had not logged on for at least two years.
This is going to change!
It's our plan to bring this gradually down to one year, with a grace period of up to a maximum of three months, as the process of deleting inactive users will probably be performed four times per year. FanDeZhi has limited resources and we want to use them for the benefit of active users, so if you want to keep your userid and datasets, make sure you log on at least once per year.