I had been thinking that Paige could not possibly get off scot-free. I wasn't thinking of DNA evidence, but that she would crack under questioning. After all, we've seen her shout "Mom!" at a crime scene, forget someone's name, and forget that she shouldn't punch people in public. However, it does make sense to me that Stan might protect her, to prevent her from revealing that he let the killer spies go. So thanks to everyone who brought up that possibility.
I do wonder what her alibi will be for that evening. Best bet is probably to admit she was on the run but say she was coerced. If she pretends she was out somewhere else, that's a whole complicated thing to make up and she'd have to explain why her ID is missing (unless she dug it up on her way back to the safe house). Then again, since she never spoke on the phone to Henry, she could plausibly claim she wasn't with P&E, but I don't see Paige being able to stick to a convincing story about where she was that night (one that holds up when the FBI checks it out, including asking Paige's friends or people at the school library or wherever she claims to have been).
I thought it was interesting that P&E never told Paige before about the escape plan. She was shocked to hear they were going to the USSR, and so flabbergasted that she couldn't comprehend that she had to pack a bag. In the 2-3 years of her spy training, they never talked to her about the possibility of fleeing the country. No wonder she hopped off the train. What American kid would agree to go into exile, on an hour's notice.
As an aside, Paige's disguise was a perfect 80s look. As she stood on the train platform looking tragic, her appearance reminded me of someone from the 80s, but I couldn't think of whom. Then it hit me:
(Mike Mills, the bass player from R.E.M., center).