FIAT money is our daily currency which has been existing here for hundreds of years, when crypto currencies like Bitcoin is squeezing their way up to become a world currency and sort. Can they co-exist? If so then what benefits we can get from them, altogether? Not separately.
Yes. Why couldn't they co-exist? They do currently and in fact likely always will. Bitcoin has become more of a speculative asset like a digital gold and that's why most of the money is going into it right now, so this is like asking can fiat and gold coexist. As for bitcoin being a currency one of my personal visions for it it to become some sort of "world currency" and hopefully it will, but right now most of the interest is coming from investors, but hopefully that will change over time and it starts to be used more as a viable currency.