- Sickness
- Disability
- Total loss of electricity (only in South Africa, thanks ANC and Jacob Zuma)
- Abduction by terrorists
- Abduction by aliens
- You go to heaven
- You go to hell
If you want your data available to your spouse, friend, loved one, or dog, then you need to ensure Google has your Inactive Account Manager settings - to do this follow this link
https://www.google.com/settings/account/inactive
and set it up - it will take you five minutes and will save your family, friend, loved one, or dog many weeks (months, or even years) of agony getting access to your personal content.
Go on, do it. It's the responsible thing to do.