Darth Vader tries tempting Luke with what seems at the moment, as the only way out. In reality it is a potential path to his undoing. Choosing the abyss in this situation seems as though it would be certain physical death for Luke but in reality accepting the path of Vader would be a spiritual suicide.  Luke was fortunate enough to take the abyss over being seduced by the dark side like his father Darth Vader was from the beginning.