But NATO is a fiction, and has been for 20 years.
The danger to Estonia is that it may be in Putin's interest to expose the fraud, which he could do at very low cost at that location.
OTOH, I doubt that causing the world to see that NATO exists on paper only alone is worth the dusty bones of a single Russian trooper.
Watch Merkel. The Germans have a lot to lose in the current state of affairs, but they have a lot to gain, potentially, as well.
People can term NATO "fiction" all you want, but these countries entered into that structure with security guarantees.