uᴉoɔʇᴉq will more then likely won't destroy fiat , Banks and goverments will simply won't let us do that . They will even make their own crypto currencies but It won't be decentralized like uᴉoɔʇᴉq because they like to control .
Now if we speak about the price , yes It's going to rise a lot and if we speak about the users then yes It will rise a lot too but "Almost everyone" ? probably not .
I also think like that a time will come that every country will have her own crypto currency as their national crypto currency, just like the fiat system. But I wish it do not happen, and everyone accept bitcoin.