Happen v. i. : To come by chance; to come without previous expectation; to fall out.

Happen v. i. : To take place; to occur.

Example:
What would Happen, if you called a retail store home office, and complain about a manager?

Taxonomy
hap, Merriam-Webster Online Dictionary, Dictionary, webster, pen, Word Games, Webster Online Dictionary with audio pronunciations, Middle English, glossary, language, ESL, Search, intransitive verb, Inflected, pened, Etymology, 14th century, mistakes will happen.

Defination from the web:
happen from the Merriam-Webster Online Dictionary with audio pronunciations, thesaurus, Word of the Day, and word games. ... 3 : to do, encounter, or attain something by or as if by chance <I happen to know the answer> ...