✔ 最佳答案
In theory, you can leave the U.S. without re-entry permit for up to 1 year.
Anytime longer than 1 year will require either a SB-1 Visa or re-entry permit to return.
However, in practice, having a re-entry permit or not will not be a matter as:
1. CBP can question your true intention for immigration at any time.
2. Unless you volunteer to do so, CBP does not have the actual authority to cancel your residence. Only EOIR (aka immigration judges) can.
In other word - the worst case is you will have to fight for it.