I had a lot of trouble finding a definitive answer to this one at Microsoft. Please take these comments of my interpretation of what happens from the following blog knowing that you may want to test this with your applications prior to deployment.
If you client falls out of compliancy in an NAP environment while you have open data from a network share, the result will be like if the server went down. Let’s say you open a Word document and are happily typing along. You client goes out of compliance and loses its connection to the network. Since the data is already loaded in Word, the user should be able to continue typing. If they try to save it, Word will not be able to access the location. They will have to save the changes locally until the client is back within compliance.