With all the laws now on the books, it wouldn't surprise me in the least bit if the NSA threatened (her) Yahoo with treason and find ways to make it stick.
If Snowden's quick exit of his own country wasn't enough to justify the claim, well, you can claim "It's not treason" all you want to, but I sure as hell wouldn't take the chance either.
Despite this, I've always said THERE IS SAFETY IN NUMBERS! EVERY company needs to come out at once and dump what they know.
Because once they do this, the NSA will have no choice but to defend themselves, and I'm pretty sure public outcry will ensue if they tried to charge every CEO with treason while covering up their law breaking violations.