If a student leaves as a Cornell alum (gets a Masters degree, say), they retain their Cornell-addressed email forever. But not many other NetID-based benefits.
Per Pat Hine's office, ~10 grads leaving with Dichtel (as of 4/29/16). This number matches up closely with group's number.
Snapshot: Dichtel group members and where they are going

Will's laptop

Currently on Cornell's Active Directory (AD) and has Cornell-licensed software

...