You could always say that he had to leave because the Sword drew him somewhere. Maybe he had to do something to strengthen the bond between himself and the sword? A lot depends on if the sword is sentient, if it contains a magic power and is bound to him, or if he has power by holding it, but to someone else it is useless (outside of having a sharp blade, that is).
Personally, I love people who have in depth and thought out backstories, so I'd love to see how yours turns out. I almost made a broadsword/super reflexes who was going to have a bond to his sword. Nice to see someone else has a mind that work ssomewhat similar to mine.
Possibly Ghost Widow wanted to take the sword for herself, to increase her own power, but found that severing you from the sword was impossible without killing you, and killing you would destroy the sword? While she was in the process of performing a VERY intricate ritual that would severe the sword from you by putting YOU in another dimension but yet leaving the sword in this one, you managed to banish her to the other dimension (or perhaps escape with yourself AND the sword at the same time - recalling it to your hand as she pushed you into the portal, perhaps?), and then escaped back into this dimension in a safe place.
Just a few thoughts.
Perhaps the villian needs to draw power from the sword, but the sword is somehow bonded to your character, so she needs him allive while she uses the power that she's drawn from the sword. Also, perhaps, she thought that she did kill him, but he managed to survive and needed time to recover before stealing his sword back. ...I'm sure you can think of something cooler than mine ideas, though.
Nilbog is goblin spelled backwards!
Anyway, a little more background would help. But maybe he lost his sword, or suffered an injury, or was in a coma. More people in comics have comas than soap opera characters.
Ack! ::covers last post with hands::
sshhhhh........
Wow with just two suggestions the story evolved 100 fold, i posted this in the right place!
The sword is sentient and it leans toward evil.
Slayer was chosen by his evlen tribe to wield it because he was the only one strong enuff of will to control it.
This story allows me option to jump to villains if ever possible 
With your suggestions I came up with a story that explains m name change, my absence, my respec and vet reward.
Ghostwidow traps Alleister and experiments with dimensional travel to seperate him from the sentient sword called Slayer. When all else fails she kills Alleister and wields the sword for herself. She instantly feels its power then it grabs a hold of her and draws energy from her. The sword uses her power to bring Alleister back to life though with its magic it puts itself into his body and traps his mind within the sword. The toon name is changed to Slayer now. In the respec i grabbed assault and vengence which is a sign of the swords mind controlling the body now. Blackwand vet power is justified with the power from draining Ghost Widow. Thank you for help 
My main is a magic bs/sr and the story premise of the character is that the sword is a magical artifact that gives him most of his power. I have been forced to be away from my puter for a few months and I would like story suggestion for my bio to explain characters absense, he is one of the leaders in sg. Was thinking of a little story about being captured by ghost widow whoam tried to sever the link between the sword and myself though the flaw is she just would have killed me lol So im open to concepts if any one is feeling creative.