Two arguments here stand out. How on earth can people abandon fiat for bitcoin when:
1. Blockchain simply cannot handle the extra 20 million transacts that will come daily (very conservative estimate). Should people wait 2 or 3 days to ensure they aren't victims of double spends?
2. Should electricy and internet get disrupted (a lot for more than half its population) are people going to simply pause trade and commerce?
The Bitcoin network could handle it and transactions would still go through fine if you just add enough fees.
There will be services who will encounter problems, but if you just send coins personally you can guarantee your transaction is included in the next block by adding more fees.
How could they possibly go through if there would be not enough room for them in the blocks? Only a small percentage of these transactions will get included with the rest being thrown away in a couple of days. Basically, it would mean that the majority of users won't be able to transact at all just because most transactions with be lost.