Trying to identify a short-story I read around 1983 or '84.
A man thinks another man sitting next to him in a bar looks familiar. As they begin talking, he realizes that the reason the man looks familiar is because he's a well-known scientist.
As the conversation continues, the scientist says that he has just discovered that the world is about to end. No one else knows about this yet. He asks the man, "If you were me, would you tell anyone?"
The man asks if there's any way that anyone could stop it from happening.
"Is there any way that anyone could escape?"
"Not unless he could get himself clear off the planet in about four hours time."
"In that case I wouldn't tell anyone."
"Good. Then I won't either," the scientist says, and gets up and leaves the bar.
The man figures he's been the victim of some kind of practical joke. Then he notices the scientist has left his watch behind.
"I'm sure this is just some kind of joke. He'll be back any minute. But he's already been gone quite a while, and it's a really expensive watch."
I think I probably read this in Omni Magazine.
Can anyone tell me the title and author?