Plot Bunny 1:
The ghostbusters go out to bust a class 6 ghost. Janine goes with them as Egon is getting over a bout of the flu. The firehouse is robbed and Egon is shot because he surprised the robbers.
Plot Bunny 2:
The ghostbusters are headed home after busting a nasty class 5 ghost. It is raining cats and dogs. A drunk driver runs a red light and t-bones Ecto-1. Egon is driving. Peter sees Egon leaning against the steering wheel with blood running down his face.
Plot Bunny 3:
Egon has been coughing up blood and keeping it a secret from Winston, Peter, and the others. They are in the middle of busting a rather slimy class 5 when Egon collapses. They find out at the hospital he has double pneumonia. (You can change it to cancer if you wish).
Plot Bunny 4:
Janine and Egon have a one-night stand. Janine is pregnant with Egon's child, but before she can tell him, he's killed during a bust.