The heath of the Presidential candidate is only an issue if the vice-presidential candidate is poor.
What hurt John McCain was not his age or health, but the fact they he picked Sarah Palin as his Veep. People felt squeamish about her having her finger on the red button,
Hillary's veep is Tim Kaine, and to be honest, I think a lot of people would prefer him to be president rather than either Hillary or Trump. So they'e going to vote for Hillary, and if she pops her clogs, they'll give her a nice funeral but will be secretly very pleased with President Kaine.