How did Mrs. Pignati die in The Pigman?

Unfortunately, readers are never given an
exact answer to this question. What we do know is that Mr. Pignati loved her very much, and he
is basically lost without her. This is probably why he allows John and Lorraine into his life
the way that he does. He is searching for some kind of companionship to replace what he had with
Conchetta. Until John and Lorraine entered his life, Mr. Pignati's best friend was Bobo the
baboon.

The loss of his wife must have completely devastated Mr. Pignati,
because he doesn't admit to John and Lorraine that she is actually dead until chapter 10.
Instead, he tells them (and perhaps himself) that his wife is away on a long trip to California.
This lie is most likely a coping and grieving mechanism for Mr. Pignati. It's emotionally easier
on him thinking that Conchetta is away rather than permanently gone.