[echlebek]

Maybe not in your dialect of English, but what about older dialects?

"Pay for your beer. Else, leave this place at once!"

[enf]

This is a usage that I have no memory of ever encountering in any context other than computer programming. It may be in some dialects, but not in ones I have come in conscious contact with.

[enf]

Actually, no, you are right: I seem to have received one email message that begins a sentence with "else" in 1996 and another in 2003. So it is not unknown to me, but it is quite rare.