No, I think that it can't. It could be used along with traditional money but it can't entirely replace it. Unfortunately bitcoin has to many issues, weeknesses and characteristics that don't allow it to be fully used and implemented in traditional financial system. Volatility is just one of them.
I agree. It could - IF there were enough bitcoins to supply 7.5 billion or so people around the world.
If fractions of bitcoin were divided among the population, that fraction would have to be worth so much as the smallest unit or satoshi would be used to purchase basic commodities. But micropayments in bitcoin is an issue now with the miners' fees and the time it takes for transactions to get confirmed. Also, some satoshis get orphaned, affecting the supply. So there really won't be enough for the whole world to share 21 million bitcoins (provided that all 21M are in circulation) and so I guess bitcoin won't replace conventional money (after all it isn't considered a currency). Perhaps some other crypto will replace money since it was foretold that future money will be digital anyway...
But, bitcoin can be a very valuable commodity - like gold or better
. So if you sell it, you could reap gains.