You can't use your bitcoin anywhere and at anytime without any restrictions like you have mentioned. Most of the stores in any country still don't accept bitcoin as a form of payment. You can't use bitcoin instantly unless the merchant is willing to accept transactions with 0 network confirmations.
And no, your money doesn't become useless. When you move to a different country, you can always use your card to make transactions and it's true sometimes it is going to take a lot to move your money from one country to another, but even if you can move bitcoin, you will have a hard time using it as a regular currency.
One has to realize the fact that Bitcoin can only play an alternative role and not the general currency in the economic systems. But also Bitcoin even in its digital form can be sent across the border and can be exchanged at various exchanges.