The odds of the two blocks hashing to the same value is about 2^256 which is about 1.15 * 10^77.

In case you don't understand scientific notation, the chance is about 1 in 115000000000000000000000000000000000000000000000000000000000000000000000000000.

The odds of being killed by a meteorite is about 1 in 250,000

http://www.wired.com/2013/02/asteroid-odds/

Odds of death by lighting are about 1 in 10,000,000.

http://www.theblaze.com/stories/2013/02/15/how-likely-are-you-to-die-from-gun-violence-this-interesting-chart-puts-it-in-perspective/

You would be better off planning for these two events.
These events are much more likely to occur.

Toshi