Although some undoubtedly died of old age, the most likely culprit was sickness. 36 hours is a long time to go without peeking in on your village!

I'll give you a little tip for the next time something like that happens. After you get your LifeDrive all back the way you want it (don't you just LOVE how long it takes to reset?), take a look at the date/time of your latest savegame file. Set the LifeDrive's clock to match, use QuickInstall to load it onto the LifeDrive, bring up Village Sim, pause the game, and then set your LifeDrive's clock back to the correct time. Voila - no dead villagers!

(This technique will work with any device, not just LifeDrives.)