I experienced(and still do)something similar, I guess. What happens to me is that I can no more call the helicopter homie, the reason is that the chopper-guy seems to be dead.
That happened when me and a friend of mine played on my save doing some testing, he used cheats without the "Hidden Cheat Enabler" by Bmhur1 but I didn't worry because I had it...And after calling the helicopter homie, the guy that brought us the chopper died. Till then I couldn't be able to summon it again. Same thing happened days later with the car dude, but when my friend left the game I didn't save the world, so now I still have the car homie.
Is that the same thing happened to you?
Does someone know what we have to modify in the save folder to bring homies back?