To be clear i don't know. I skimmed through the EULA and didn't see anything definitive. However, I suspect that Microsoft is giving 10 away for the reason of encouraging fast user migration to 10. If they permit users to go back to 7 at any time, then it would seem that they didn't accomplish their goal. Stated differently, I speculate that Microsoft would want to configure their free deal as a transfer (or relinquishment) of your original 7 license in return for a Win 10 license. Does this make sense or am I not looking at this correctly?