The reset button syndrome is a retconning tactic whose use is probably most often ascribed to writers of Star Trek Voyager or TNG, but it can be used in all forms of literature to get out of a corner one has written oneself into.

A good non-Trek example of the syndrome is the return of Patrick Duffy to the old nighttime soap opera Dallas. The actor left the show for a year, and his character, Bobby Ewing, was killed by a crazed hit and run driver (just don't ask, okay?).

After Bobby died, the other characters all reacted as one would expect should their husband, or brother, or mortal enemy had died. However, a year later, the show's season-ending cliffhanger ended with Victoria Principal's character, Pam Ewing, waking up one morning to find a very chipper and very alive Bobby taking a shower.

Viewers had to wait several months to find out that the entire previous year's worth of episodes had all been a dream. In essence, the writers hit the reset button, eliminating all the plots and character development that had taken place during Duffy's absence.

Needless to say, the viewers felt quite cheated and a huge stink was raised. I'm sure they would have accepted an evil, but heretofore unknown, twin brother more readily. That, at least, is a well-established plot device to bring a presumed dead soap opera character back to life.