'He died from fear. The fear of it killed him.'

Agree!

Why would he be in this movie anyway. He didn't want to be in the 2nd one.

Lol I didn't say it was a brilliant reason.

Because Sid Sheinberg is a very selfish egotistical man. He wanted Gary (his wife) to be the hero in part 2 (or at least sidekick) but was told "over my dead body". The fact is Ellen Brody was always meant to be the loving supportive wife character. So when he became head of studio, he decided his wife was going to be the hero and star of the movie despite others wishes and what the fans wanted. Basically his wife was going to be the lead and no one could stop him because he was in charge. So he did whatever he could to be sure the movie would always be focused on his wife. The first act was to kill off the real star and fan favourite of the movie (Martin Brody) so his wife could be the full focus. As you can see the original script called for our favourite character to be killed off easily by a shark after all he'd went through in the first two movies, just so his wife could be the star. Luckily Roy declined so Sean was killed instead. But basically they said Brody had died of a heart attack, just so his wife could take center stage.
I mean a 50+ unattractive actress at the helm of an action picture? How often does this happen. Nepotism at its best

Ya know... that might actually work. Keeps the action in Amity - who cares if it's winter time - they could skip ahead a few months if they want to film in sunnier weather - and Amity, imo, is the crucial as well as the nostalgic setting. There could be scenes showing the different behaviors/reactions of the locals to Chief Brody's death-by-shark, and there could be a nod to the Spielberg film when the actual hunt starts - some Amity hunters are responsible, others shouldn't be on the water at all, some are sneaky and greedy... Congrats on coming up with an interesting scenario.

OT: as others have said, I would much rather have had Schieder come back and Brody get killed in the first part of the film. The audience would really feel the pain, and cheer that much more the town's concerted effort to kill the shark. And Brody could have been killed just a little later in the film than his son does in the current movie - that would build more sympathy and stir nostalgic memories of Brody from the first two films. Again, as a poster said, it's far more realistic and appropriate for Brody's character to be killed by a shark, rather than die off-screen of a generalized shark-fear heart attack.