Yes, Clinton has health problems, but she's still alive.
If her health were really bad, the VP pick would have been a lot more impressive than that sock puppet Tim Kaine.
I would argue that the Clintonistas would want someone controllable.
Recall, they are already fighting with Obama’s people over long term control of the party.
Also, they would probably hope Hillary would survive 2-3 years (been less than 2) ... so Kaine could be elected twice. That would give them the time to bury Obama’s hopes of remaking the party his own as the Clintons did during the 90s and during W’s tenure.