For any large amount of data doing it in house is hugely and I mean hugely cheaper. Over a five year period 500TB in the cloud will cost over two million USD. For that sort of money you can buy the storage build a data centre and pay the staff and still have a significant amount of money left over. Then for the next five years the data centre comes free.
Then there is the simple fact that there is insufficient manufacturing capacity for flash to change the equation radically in the near future. It takes at least a couple of years to bring a fab online so capacity is known for some time ahead. Flash manufacturing capacity is only a couple of percent for hard disk capacity let alone tape.
Also where are the cloud providers going to store this data? Magic pixie dust or something?
In short neither disk or tape is going anywhere fast.