For one thing, many governments will have laws about availability of key infrastructure (roads, snail mail, 4G and 5G, wired internet, financial services etc.) which result in resilience decisions:
* Have at least 2 or 3 mobile networks; if 1 fails, people can still dial 112 (911) over the remaining one(s)
* If banks break down, you can still withdraw up to €xyz from an ATM during the emergency
* Even if all mail isn't delivered on all days, letters from the government or letters announcing someone died are still delivered
* If a city is "serviced" by two highways they can't both be closed at the same time
* Etc.
In some countries, governments (or utilities etc.) use WhatsApp in critical processes and communication. So just like the things above, WA should be considered in these contingency plans. Stuff like:
* WhatsApp cannot be the only contact info agencies have - they need at least a backup contact method
* Facebook should announce maintenance activities to WA to these governments in a standardized fashion
* Facebook has to commit to keeping (the main functionality of) WA free of charge
* Etc.
If Facebook doesn't want to commit to stuff like that - fine, but then the consequence should be that WA is no longer considered a valid tool for critical communication, as Facebook then clearly sees it as a "hobby app" that can go down for hours without real consequence.
With great power comes great responsibility.