Fiat is fiat. For now nothing can replace it.
well not true, you can replace it already at least partially , there are some services that offer you to pay in bitcoin, to receive what you want
Well it is true, but bitcoin will always be valuable, and I think if that happens, you just have to ask the person bitcoin wallets address, and send it in place, the point you just have to bring your running bitcoin wallet that you can download on your smartphone