I actually think Sasuke has a response to being stabbed in the chest. While this is technically a critical injury, Sasuke did just get some sort of upgrade from Hashirama. Furthermore, Sasuke potentially can use Izanagi. He watched Danzo use it almost a dozen times and could have also learned if from Obito or Itachi.
I have no doubt that Naruto is going to come back stronger at some point, and the Tailed Beasts are not gone yet, either, but Gaara's plan is likely going to take time to execute, and in the mean time, I think that Sasuke is actually going to get a chance to shine. Why else would Kishi make such a big deal out of Sasuke looking like Izuna and Hashirama giving him some sort of Sage Mode cancelling technique?