Gap said:
There was no certainty that Saul's sister had anything for Carrie and even if she did that it would relate to the interpreter asset. That was hope and desperation by Carrie.
The whole thing even from the GRU's end was hope and desperation. They wanted her to kill Saul simply hoping that Carrie was who she would be handed over to, and while likely, there was no realistic timetable on how long that would take to happen and by what means. For all they knew it was the interpreter that had been told that if Saul dies to do 'xyz' a month or six months after.
The whole last 2 episodes really just seem like they existed on their own. Suddenly we create this russian asset and a Saul backstory, then... what can Carrie do that is the ultimate betrayal? Ooooh, lets set it up so she has to kill Saul. But killing Saul is too dark for this show to end on, so we'll make everyone think she's killed him then walk it back.
I only shortly gave up on the show before coming back, because it is still a very well acted series that can be exciting at times... But man oh man the writing just wasn't up to snuff.