Stage 17 is where Jumbo need to earn their keep in this race. They need to keep the race together for a reduced group finish. If they can accomplish that, Roglic probably gains at least 10 seconds on Remco, given the latter's lack of finishing sprint and the former's strong final kick. That get's Roglic 10 seconds closer. Stage 19, another chance for Roglic to gain more time. If Primož has the legs I wouldn't be shocked to see him attack towards the top of penultimate climb of the day. Regardless, even 30 seconds here would feel like a win for Roglic. In stage 20, unless Remco is suffering, you have to attack early. Cotos is sort of a soft climb to put much time in someone who is on their game. If I am Roglic, I isolate Remco and then attack on the Morcuera which is steepest towards the top.
Either way, Roglic has 2 mild but 3rd week mountain stages to make up probably about a minute 20. Then a hilly finish to hopefully get another 10-15 seconds.
Of course, how much fun with it be to see Roglic sprinting for time bonus in Madrid to try and win the Vuelta. The sprinters will be gassed by then, the fastest sprinter in the race is out of it and Roglic has a kick. It could come down to that. Now that would be must see TV.