No cash will never be extinct because there are always some country's that are poor and don't have internet so they need a form of payment method to buy their stuff. So that is why cash will never go extinct.

I don't think that bitcoin will end as long as there are people who believe in bitcoin and invest in it. so you should keep investing in bitcoin as long as you can.
Then you will be happy with the profit you will get.

Holding your bitcoin is a way to invest in bitcoin because the value is rising so you make bitcoin by actually doing nothing. This is also the easiest way to make yourself some bitcoin otherwise you can go trade.