Mike BD :
If I'm an Insider that currently runs build 10166 from Microsoft,will I be able to download the RTM as ISO from them?
Your Tech Preview will roll over to the same version as the actual release, on or after July 29.
Can you d/l an ISO for that? Unknown, but probably.
But to continue using the Tech Preview, you must remain a participant in the Insider Program. With all that entails. In effect, being a permanent beta tester.
If you choose to opt out of the Insider Program, either you must go back to Win 7/8, or purchase Win 10 on its own.
http://blogs.windows.com/bloggingwindows/2015/06/19/upcoming-changes-to-windows-10-insider-preview-builds/