I think 90 is a bit high, simply because I'm not sure the chances of Clinton having a stroke or plane crash or whatever between now and July are sub-10%. Eight months is a long time to just blithely assume someone will remain in good health. Just IMO.
Really? If you look at the percentage of healthyish 68 year olds who die or suffer a very serious illness within a year, I am sure it would be far less than 10%. And Hillary easily seems at least of average health for her age, as well as obviously having access to the best of medical treatments).
(As for the risk of assasination or something like that, I can't see it as being plausible enough to affect the odds at all)