BTC is not going to be worth 1 million a coin in 2 years. That is where you are wrong so the rest of your argument makes no sense.
oh, also, and if it were, the block reward would no longer be 25 BTC. It would be 12.5 BTC.
Why?
Well, a 2,000 fold increase in the price of bitcoin would cause a huge demand in mining. You agree since you believe people would spend 3.6 billion per day mining.
Right now many ASICs can achieve 1 GH/s per watt of power. Let's assume ASICs don't get more efficient (they will) and assume an average electricity of $0.15 kwh. 3.6 billion dollars a day in electricity is enough for 1 TRILLION watts of power. or a total network hashrate of 1 x 10^12 * 1 x 10^9 = 10^21 or 1 zettahash/s worldwide hash rate. The current world hashrate is roughly 10 petahashes (1 x 10^16). That means the world hashrate would have to increase by 10^21/10^16 = 10^5 = 100,000 times. This would make the difficulty be around 100 trillion.
This would mean the world hashrate would have to double roughly 17 times. The hashrate would have to increase at such a ridiculously high rate that we would got through blocks so quickly that we would hit the next block having date in far less than two years from now. Thus the block reward would only be 12.5 BTC.
I'm too lazy to actually calculate how long it would take to hit the next halving. I'll let someone else do it.
We're gonna have a "party" a few months earlier.