We don't know anything about how severe his complications are.
It is fully possible that he could keep working in a reduced capacity on the state council. But if he has had anything that would make him less verbally articulate, give him difficulties with understanding audio or other issues which would make it hard for him to do diplomacy, it would not be reasonable to take him around the world and let him meet foreign diplomats.
Because while China itself can provide his special accommandations at home, as a foreign minister, he would not only have way more workload, but he'd also need to travel to other countries, some of which won't have the same accommandations.
My speculative guess is that he has suffered lifelong consequences. Allowing him to keep working is the government's way of honoring his legacy and allowing a smooth exit rather than immediate retirement due to health issues, but he isn't going to be anywhere near his peak condition anymore.
