As long as it isn't Trump. He has to take the high road here and do nothing other than wish her well. Res ipsa loquitur.
In the short run perhaps. But on the campaign trail, Trump must continue to call Hillary weak and lacking the stamina to hold office. Hopefully, Trump will not fall into the trap of giving Hillary a pass similar to what McCain and Romney did with Obama. No doubt the subject will come up at the debates.
Also, his camp can call for her complete medical records without Trump releasing his as well.
Better that she limp along to election day IMO than risk some last-minute replacement who might get sympathy/rallying votes.