Every event depicted in the story is canonical
The Mind Screw ending comes about because Pat Conley was Not Quite Deader Than Dead after Jory ate her. When Chip fights Jory, Jory is weakened enough that Pat's soul regains its powers and, understandably unhappy with the turn events have taken, rewrites history so she never died. The potential for far-reaching changes was established during her interview, in which she temporarily rewrote the preceding year (in direct contradiction to her later claims that her power was relatively limited. If Jory is to be believed, she thought she was in charge.) This requires that psychic powers can affect the living world from half-life, which is established early on when Jory appears to one of the psychics in a dream. To recap: after the assassination attempt on the moon, everybody but Glen Runciter was killed and put in cold pac. They were placed in the same morgue as Ella Runciter and Jory. While everybody in half-life tried to figure out Jory's Lotus-Eater Machine, Glen attempted to contact them. Chip's strong will gave him enough localized power over the hallucination to weaken Jory as described above. When Pat made her move, the timeline changed so that only Glen Runciter died, and Chip, as the executor of his will, attempted to contact him.- Just to make this even more Mind Screw, due to one of his other works, Our Friends from Frolix Nine, we know the fact that God died in 2019 (they found his corpse). When is Ubik set? 2019!
Hollister had Melipone killed at the beginning
Jory's family is supported by Hollister's syndicate, and Melipone was payment in advance for the extra strain that Jory would be under when the inertials were added to the morgue. Because the psychic vampires gain the powers of those they consume, this effectively gives Hollister a more powerful agent at a lower overall cost, capable of cloaking themselves from pursuit by prudence organizations. Ubik was a trial balloon for Product Placement in publishing
Ever seen the artwork for the original hardcover, with the aerosol can? The ad agency for Ubik Deodorant—due to Glen Runciter died at the end, but in the same timeline
We only are offered glimpses of what happens to Runciter while the rest of the team is put on coldpac. However, we do know that he is planning to proceed legally against Ray Hollis because of what happened. Since he's still mourning, he put everything on hold for a day to start the process. It is at this point that Hollis, using one of his agents, decides not to leave loose ends, and kills Runciter. With him being close to the Moratorium, he's quickly transferred to the coldpac, which is the final scene we see.