You presume that Putin would be willing to make that gamble, which seems unlikely.
Russia is far too busy with Ukraine to do anything so silly & likely will be for some time to come. Radicals from western Ukraine & complete disarray in Kiev gave Putin the opportunity to act, & he did. No parallel situation exists in Estonia. They have their shit together a lot better than Ukraine ever dreamed of.
Hell yea I'd like Putin not to make that gamble. But honestly I think if he does NATO will most certainly flinch.
I don't believe Russia has that much involvement in Ukraine. Yes, they are involved, but not close to the full force of their military. They have the ability to start trouble in Estonia if they so desired.
Yes Estonia has their shit together with a much better economy, I believe their gdp per capita ratio is better than Russia's. But they don't have everything together, they treat the Russian population within the borders as second-class citizens, including, for an example, denying access to obtain Estonian passports even if they were born in and raised in Estonia. They are forced to look to Russia for support.
http://www.npr.org/templates/story/story.php?storyId=129333023
I'm also friends with someone who is half-Russian, half-Ukranian, born in Estonia, now lives in the U.S. permanently. I've asked about conditions there. That part of the world simply cannot figure out how to live peacefully with their neighbors.
The Soviet Union tried their best to remove the ethnic groups and cultures of all these countries replacing them with Russians once before. I didn't think Russia would get involved in the fight for Eastern Ukraine. But they are. And Putin is calling the territory New Russia (in Russian, of course).