As difficulty increases the price naturally will go up and the only reason why we're not in $1500 range price is because the uncertainty caused by BU and the possibility of a hard fork.
Fiat doesn't need to go any where and we're good as long as people willing to pay fiat in exchange for bitcoin for now.
Bitcoin is not a replacement nor an alternative for fiat but just a new kind of currency which could be obtained in a decentralized manner.
If you want ETH and LTC then go start mining them while it's much easier than bitcoin mining.
man you are confusing the two thing, difficulty go up when the price increase, the difficulty always follow the price, if it was like you said the mining would be unprofitable, because there will be no guaranteed that the price will increase after the diff increase, recently the diff increased again because the value went up this prove the theory