Near the end of the 2018 version of A Star is Born, Ally says to Jackson that she will have a car come pick him up for her show.
We then see Jackson getting in his truck to go to the show. Was there ever a car coming for him?
Jackson wasn't getting into his truck to go to the show, he was moving his truck out of the garage to make room for him to hang himself.
Ally had just blown off her European tour to be with Jack after his return from rehab. If you recall, her manager declined her request to get Jack on her tour so she could continue to be with him. Jack was not only battling his alcoholism, but his immense shame for embarrassing her at the Grammy's, and had also been told by her manager how his behavior had almost completely destroyed her career. This sent him over the edge and led him to finally commit suicide.
After Ally said she'd send a car for him, he mumbled (barely audibly), "I'll just meet you there." So, yes, she would have sent a car for him but, for all intents and purposes, he told her not to bother.