This is a good point, it is important not to underestimate the hold which the Thalmor have over the Empire. However, if the Blades were to be discovered and agitated by the Thalmor alone, without Imperial knowledge or negotiation, it is possible that the Dominion would see fit to take care of the problem themselves instead of trying to force the already-delicate Empire to get involved. It almost seems like the Thalmor have a personal vendetta with the Blades (even greater than that for the Empire), and they only used the Empire to do their dirty work during the Concordat negotiations. Since the war for the Empire has pretty much been won, the Thalmor might be more likely to deal with the acute threats like the Blades without Imperial involvement. yes i think you right also you could also have something like nearby thalmor troop movements spot sky-haven and decide to check it out and so parthurnax comes and tells you and you have to intercept there messenger before the rest of the thalmor find out then the dragon born has to go defend sky-haven or it could even be that visiting the temple a certain number of times sets this off minus parthurnax