It really depends on how the home was prepared before it was left. If it was done professionally or the right way by someone, the damage, if any would be minimal.
On the other hand, if the property was just abandoned without any measures taken to protect the home from the elements, you can expect there to be considerable damage.
Our advice is to find an experienced agent or an attorney that can "wordsmith" a contingency clause that will protect your interests and give you an escape route if things get out of hand.
The Eckler Team
That being said, a property sitting vacant for 6 months would not scare me away. If the property is built and winterized well it should be OK. I have a property in our "HomeWatch" program that has been for sale for over 3 years, and it has never had any major problems. I check up on it once a week...every week...for over 3 years now...[It's not my listing- if it were I would have sold it by now :-p ]