I wonder what the costs involved would be to have backup power generators for each of the towers. I think it would be more cost effective to have people with mobile phones as walking towers then having a tower run for X amount of time and then you lost your connection. Not sure if either method would pan out though in the great scheme of things. I guess you'll know what method would work best ones your facing a disaster scenario first hand.

As they say, sometimes you have to go for the lesser evil.

Unless the app can turn your phone into more of a p2p network where everyone would be connected all at ones using wifi turning all phones into towers themselves for people to connect to and share what info they need to.