What happens to indoor coverage during emergencies?

A very quick question:

- Which of the current crop of indoor mobile coverage options offers the best chance of working during emergencies, for voice and/or data?

Historically, landline phones have been fairly reliable as the lines are powered from the exchange (unless it's via a locally-powered PBX or home cordless unit), and have a direct physical metal connection exiting the property through the wall.

Conventional macrocellular 2G/3G phones and networks have also been to individual buildings being affected, although city-wide events such as terrorism and earthquakes have caused congestion or failure. The use of GSM or CDMA in 850-900MHz and 1800-1900MHz bands has tended to mean reasonable indoor coverage.

But I'm wondering if newer solutions such as WiFi, femtocells and even active distributed antennas & repeaters are more vulnerable, as they are reliant on local power from electrical sockets and the in-building LAN wiring and infrastructure.

I'll readily admit that this isn't a focus area of mine - but with the advent of technologies like LTE & WiMAX running in high-band frequencies like 2.6GHz, reliable in-building operation surely becomes much more of an issue.

What are the knock-on impacts on both indoor build-out (UPS power for femtos?) and also specrum policy?