Recently we through the switch from Mac.com to Me.com. Due to this switch, there have been some irregularities in account handling and extensions. Some of this was due to Apple giving free service for months due to issues with accounts.
When things are running normally if you will, my understanding is that when a trial or regular membership expires, you will have a time period to renew your account. Not sure what the timeframe is, but I believe somewhere between 30-90 days.
After that, your account cannot be reactivated.
Also, once you give up your account, the user ID cannot be used in the future by someone else.
YMMV.