Who would buy my bitcoin? (Hypothetical question) Lets say if 1 BTC = $1000USD tomorrow and I have around 1000 BTC, how would I sell my 1000 BTC to put $1,000,000USD in my bank account? 

Even a better hypothetical question.

If I go back in time and buy 10,000 bitcoins for half a dollar (USD) back in 2009 and wish to cash it on 2013 when 1BTC was around a grand, whom or how would I sell all my BTCs to get the maximum profit? How much should I have paid in taxes?
A lot of exchangers have such liquidity but you will encounter issues with withdrawal limits depending on your verification level. Also I don't think you can expect transfers of that magnitude to happen at once - they will likely chunk it out by agreeing it with you.

As for the tax, it all depends where you live as I believe you will be taxed on income.

We all wish we could go back in time - however you have to look to the future, what tells you 1 Bitcoin won't be worth $100,000 in 5 years time?