I have the same problem, I have Johnny's Porsche and I called Rouge and she is in front of Afterlife, I pull up in the Porsche. (it doesn't matter what vehicle i drive) every time i start the dialogue the car is gone, i can't request a new one. She also walks towards the place where the car should be, she asks where I got the car from, but since there is no car there, she turns around and goes to her place. As I walk around the afterlife now she's really pissed off and yeah.. that's it.. I have no idea how i hold my car as long as the dialog is finushed... And yes i load save points from before, it doesnt work