What happened to Emily Bennett after Katherine was "death" ??

You mean dead? She lived her life.

Damon would protect Emily's descendants and Emily would use her grimoire to protect Katherine by entombing her with 26 other vampires under the old Fell's Church. She was later burned at the stake by the Founding Families and her possessions, including her grimoire, were taken and buried in Giuseppe Salvatore's grave. Damon rescued Emily's children when the townspeople came for her.Wikipedia, section Emily Bennet