What happens when my Unity 4 30 day trial expires?

I am interested in using Navmeshes and other pro features while I have the 30 day trial but I was wondering what will happen when my trial expires when I have to go back to working with the indie version and my project contains features from the pro version. Will I still be able to open the project with the indie version and work on it and would the pro features still work?

The 30-day trial allows you to evaluate Unity Pro and come to a purchase decision. If you decide that the Pro features are not for you, then revert to using free. As Kryptos says, the Pro features will be disabled. You should still be able to open the project but will want to go through your artwork and scripts and remove the un-wanted Pro features. In general, if you know you do not want to purchase Pro then don’t start the trial. Save the Pro trial for some point in the future when you might want to purchase Pro.