You will need to retain your old license key just in case. The RTM build will come in as another flight but you will need to specify you want to leave the program after getting it. If you fail to do this before the next unstable build (insider preview will be ongoing after Windows 10), your PC will automatically upgrade itself to that unstable build.
[Edited by Neo7, 7/8/2015 7:56:39 AM]
This isn't anything new. Microsoft was extremely transparent through their licensing agreement and Gabe Aul has posted what kind of data the telemetry data contains:
The user can turn that off on the production release of Windows 10 but insider preview users will have it turned on by force as per their agreement with the Insider Program. Again users have the choice to exit the program when the production build rolls out and then they will gain the ability to turn off the telemetry data.
[Edited by Neo7, 7/8/2015 8:19:52 PM]