Aliens... with extraterrestrial quantum computers! I heard they sell them for 500kBTC!
You can do an asic design for considerably less than 500K btc and all it takes is 10 year old cmos technology. No aliens needed.
hm...
BTC owed 500,000
Interest per day BTC 5000
Generated BTC per day 6x24x50 = 7200
So he would only need to generate 69% of all Bitcoins to make good for the interest, without paying back anything of the debt.
I would also point out that was as of the day he shut down. He owes closed to 550K BTC (and 5.5K BTC per day in interest) today. In a month he will owe ~723K BTC and daily interest will be more than the number of coins minted each day.