generalfrevious;
What would happen if Darth Vader was resurrected at the end of Episode VII?
Here's something the board may not expect from me; That could work if done properly. No different than Batman being a symbol of good, with the man under the mask remaining unknown.
In this new film they're obviously aware of who he was, as well as it appearing there are many people who want to see the Empire survive. No reason a particularly mean or ambitious person couldn't be pushed into taking up the identity thirty years later.
Darth Vader could easily become a similar type of symbol for evil. Moved away from the original storyline of our heroes and familial connections, he could be a bad person continuing the tradition of fear and war mongering. Wouldn't even have to have Empire or First Order connections.