A "Duldung" is not a residence permit but rather the suspension of your deportation obligation. Having a "Duldung" does not eliminate your obligation to leave Germany, but only postpones it for a specific period.
After the expiration or revocation of your "Duldung", in principle, you may be deported. Your deportation then may be carried out immediately and without any notice (“Abschiebungsandrohung”). Only if you have lived with a "Duldung" for more than a year, the authorities are obliged to notify you of your imminent deportation at least one month in advance. In this case, you will be sent a deportation notice or “Abschiebungsandrohung“ unless you have a “Duldung” according to §60b Asylum Act.