According to this you get RTL when you lost your ROA.
http://www.immd.gov.hk/ehtml/topical_3_1.htm
Right to land
If a person loses his ROA, he will automatically acquire the right to land in the HKSAR.
The right to land (RTL) in the HKSAR means :-
The Right .....
* to land in the HKSAR
* to be free from any condition of stay (including a limit of stay) in the HKSAR; and
* not to be removed from the HKSAR.