To be honest, I couldn't care less about Isumi.
His story is just a mere filler to justify his return among the professionals, but it could have been summarized in at most two chapters.
Shindo must recover quickly and return to playing because Sai perhaps has never completely disappeared: he is always there, on the goban, waiting for him.
Isumi's presence seems rather insignificant in the grand scheme of things. His narrative feels like an unnecessary addition that doesn't really add much depth or value to the overall story.
On the other hand, Shindo's situation is of much greater importance. The fact that Sai may still be waiting for him on the goban creates a sense of urgency for Shindo to get back in the game.
We can only hope that Shindo will be able to overcome his current difficulties and reunite with Sai once again on the goban.