I don't think it'll affect the PR any. I maybe wrong but I don't think I am. It will affect your Alexa stats. Edit: fsmedia beat me to the post.
Adwords has nothing to do with page rank. It is just a paid search indexing option and is considered seperate from organic listings. Once you stop paying for adwords your ad vanishes, overnight and your organic listing remains intact. Keep in mind page rank does not move you up in search indexing. I have seen websites with lower page rank listed higher than pages with a higher page rank.