system
Given the following post, respond as if you're commenting on Reddit:
human
[Star Wars] What would Vader have done had he survived the destruction of the second Deathstar?
gpt
It's an interesting question because Darth Vader didn't die when the second Death Star exploded, but minutes before, in the audience of the Emperor, when he chose to defend his son and sacrifice himself to save Luke - that's the moment when Darth Vader dies.  Anakin Skywalker dies a few minutes later from his (extensive) injuries on the ramp of a shuttle, just prior to Luke's successful escape.  Lets look at it from both angles, though:

1.  Darth Vader survives - Upon finally overthrowing his master and patting himself on the back for installing basic electrical grounding in his armor, since he'd seen Palpatine's lightning attacks before.  Lets just say for the sake of simplicity that Luke left in the confusion and we don't get an immediate round II with Vader.  Vader, ever a survivor, realizes that the Death Star is beyond saving and makes his way to his personal fighter or escape craft.  He links up with the remnants of the (still very formidable) Imperial Fleet and makes his way to Coruscant, where he consolidates his power while undergoing extensive repairs and upgrades.  He recalls Mara Jade, and puts her on the path to assassinating Luke.  He's able to maintain the coherence of the overall Imperial sphere through use of brutal force and crushes a few outlying Imperial rogues who want to set themselves up as small independent operations.  This keeps the Rebels from swinging in and taking apart the Imperial Fleet piece by piece, and upon the return of Grand Admiral Thrawn's task-force, the Rebels and the Empire have another massive blowout, this time with massive losses on both sides.  Luke by this point has gathered other potential Force sensitive candidates to the cause and may have even put together a small fighting force of them, but Darth has done the same, leading to significant casualties and serious collateral damage.  Likely outcome - both the Empire and the Rebels are critically damaged and a third power base comes in to sweep up.  Vader, Mara, Luke, Leia, Han, Lando are all likely dead or seriously injured.  

Edit:  Forgot to mention in this scenario that weapons like the SunCrusher would come into play, solidly in Imperial hands.  Upgrade the destruction level between Empire and Rebellion to catastrophic, including the likely loss of Coruscant.  

2.  Anakin Skywalker survives - Anakin pops up and realizes that the best thing for lava burns over 95% of the body was a good old fashioned tasering, and all the sudden feels right as rain.  The light side of the Force, again flowing through its champion of Balance, empowers him to get himself up and out of the Death Star.  Rather than link up with the Rebels or the Empire, he goes on walk-about, visiting the homes of Ben Kenobi and of Yoda, hoping to find wisdom and perhaps some forgiveness from his old masters. After years of meditation, soul searching and healing through the Light side of the force, he begins to reach out with his feelings for his children, who find their way to Dagobah and (quite surprisingly) meet with their father.  Leia is deeply conflicted and initially rejects him, but Luke's experiences with the Dark Side, and last moments with him in the Death Star, allow him to forgive.  The newly founded Jedi Order established by Luke benefits massively from the knowledge of an original Jedi and, in the fullness of time, Anakin joins his former Jedi brothers, bathed in Light for all eternity, forgiven of his sins.