If you just walk away you are still legally liable. Best case is they do nothing. Next best case is they report it and your credit rating goes in the toilet. Worst case would be a few years down the road (once the past due payments build up to the point where it makes it worthwhile) they sue you, win a judgement, and force foreclosure of some other property that you own in order to collect.
So that's best and worst. What's most likely? Even though it is possible, it is not likely that they would go to the expense to sue you. Most likely scenario is that they just report it to the credit agencies. If you don't really care much about your credit rating then that won't concern you. If you do, then it is almost never a good idea to just walk away from an obligation.
.
