u/rcgldr

The Endurance is in orbit about Mann's planet, which is in orbit around the black hole. They would have first done a slingshot like maneuver to escape from Mann's planet into a high velocity elliptical orbit around Gargantua, then slingshot maneuver around Gargantua, after which Cooper and TARS ships would have continued in a high energy elliptical orbit, rather than fall into Gargantua, despite detaching from the Endurance.