In American Reunion (2012), we learn that Jim's mom is dead. Is there any info or clue in the movie about how she died?
Director/writer Jon Hurwitz explains "why" (but not "how") Jim's mom died in this interview:
The first decision that we made literally was to kill off Jim’s mom. And we liked that for two reasons.
One, we liked how that matured the franchise in a certain way, where it’s not just about sex and losing your virginity and the smaller things in life you see in the earlier films;
When you get to be in your 30s, some serious things can happen to you, and we wanted to explore that with a relationship that you know and love.
Jim and his father have always had this relationship where his dad is giving him advice and helping him along in life, and when you reach your 30s, you no longer see your parents as just “mom” and “dad”—you see them as actual, real people. You start giving them advice, and we loved that role reversal.
The second thing we loved about it was the ability to, by making Jim’s dad single, unleash him into the world in a whole different kind of way.
Instead of just staying inside the house, he’s able to go to the party and mix it up. We were able to pair Jim’s dad with Stifler’s mom; [...] It was too tempting not to have Jim’s dad and Stifler’s mom get together on screen and see what kind of magic we could have.