Though it's not likely gonna ever happen, but if this would really happen then I would sell all of my bitcoin, because I don't think it would stay in $1M for a long time. I'm sure when this happen people will also sell their bitcoin and that makes bitcoin price drop hard.
Well we can't and we can say that this is possible as the price of bitcoin is keep on changing and that is why many investors are starting to invest with it because of its fluctuations. And if that happens then for sure that is going to make me rich and I would definitely sell all of it. But in reality if the price reached $1,000 I would sell my bitcoins immediately.
What will you do after the day you will be selling all your bitcoin for $1000, bitcoin prices hitting $2000 or $2500 prices. Never get yourself out of the race. Selling all your bitcoin at one price will definitely will make you regret in future.
So, plan up to sell our bitcoins like for your immediate requirement or any inevitable needs. Holding bitcoin will be always beneficial like it may $ 1 million prices also.