when people have only a bitcoin, and they do not save real money. while they have to pay a lot of bills and utilities. this is what must be our consideration in the future. there must be a balance between bitcoin ownership and real money. probably around 50:50 to make us comfortable in living their daily lives.
Then we back to the old method of exchange yup the barter system, it has been used for centuries and long before money and bitcoin were invented. So if someday there would be a destruction or something that makes the internet die, like you asked i think that's not a big deal for the people because we've passed this, however the gold's value would be increased due to this case that's why investing in gold for long term investment is a good choice to protect your wealth, so maybe the alternative is gold and other precious metals for payment purpose.