I assume you are selling a property with an assumable mortgage. 1st step would be to check with your lender to see if it is assumable by qualifying or not? Also check with an experienced AB lawyer (ie. Barry Mcguire @ Ritchie Mill) to see if you could be on the hook or not. He had a great presentation on this subject 2 weeks ago at the Calgary conference and I believe that yes you can be off the hook (depending on if it is personal or corporate), but your credit rating could be severely damaged if the mortgage were in default.
Best to check with an experienced lawyer and mortgage broker!!