What If.....
What if Obi Wan comes back in a later season - and is involved in a huge battle at the end of say... season 4. Lets say it boils down to Obi-Wan AND Ahsoka Vs Darth Vader. Lets say Darth Vader ends up killing Ahsoka in this battle, and Obi Wan escapes, unable to handle Vader's rising power on his own. Vader is pissed, because the part of him that was still good, didn't WANT to kill Ahsoka. But having Obi-Wan there blinded Vader in rage and he virtually had no choice. He blames Obi-Wan for Ahsoka's death.
Fast Forward to Episode 4:
Vader sensing Obi-Wan's presense : ..."A presense I've not felt since........"
He's remembering Ahsoka.
Mind = Blown!