Microsoft has now clarified about what happens when the Windows 10 builds reach to RTM stage. It seems the Windows Insiders will have option to stay with RTM build, if they wish to choose it or will keep getting newer builds, if they want to continue with their participation in the preview.
@RafaelMateusM Both. You’ll upgrade to final version, and have the option to stay there or to keep getting new builds as an Insider.
— Gabriel Aul (@GabeAul) May 5, 2015
This clarification will be welcomed by many who had wondered whether the Windows Insider program will be discontinued after RTM stage. At the sometime many may want to cease their participation in the Insider program, once they will receive the final RTM build.