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?
If electricy and internet should get disrupted then you can further pay with fiat of course but in a globalized and interconnected world as today, it will cause an economical crash and disruption. So that bitcoin can no longer be used as a payment then, is one of the smallest problems in such a situation I guess.
And it is not meant to use Bitcoin as a daily payment option but rather to save value in times of hyperinflation.