It's pretty obvious they've left it open for a sequel. The ending pretty much screamed "there's a sequel coming" with Arnie walking in all liquid metal and stuff. It also leaves it open for Arnie to be able to do another since with the liquid metal T-800, they can use a lot more CGI with him to compensate for his aging body not being able to physically do as much (which I don't really look forward to).
Plus they 'stopped' Skynet in Terminator 2, as well as Terminator 3 essentially saying "do what you want, you can't stop this from happening, only postpone the inevitable". Essentially, they can and will find a new way to keep the plot going even though they've stopped Skynet/Genysis. The fact that the liquid metal vats survived (as evidenced by Arnie being alive) leaves it open for something to happen, as well as Arnie still being alive meaning that the chip and the terminator skeletons are still existent (which is the whole plot of Terminator 2).
They also have the possibility of a prequel, with a younger Sarah Connor during the events told in Genysis where the T-1000 comes to kill her at the cabin as a child and the T-800 coming to save her. There's definitely enough for a movie there.
