The OP's question will likely lead to a similar answer in general, namely that no one knows the future of bitcoin whether it reaches $1M, $2M or more. I only hope that bitcoin will continue to grow and always be accepted by the wider community and adopted as a payment system. If adoption increases and continues to grow, the price will be maintained even though the volatility cant be eliminated.
If bitcoin reaches the price of $1M then I believe the government's involvement in regulatory matters will be higher and they will probably regulate it more tighter. Maybe I will be the reader of thousands of communities who are disappointed that they don't buy bitcoin today if the price reached $1M in the future. LOL
That's certainly true, mate. No one knows what Bitcoin's price will be in the future. Everything is just speculation. Bitcoin's value is determined by everyday people like you and me. That's because Bitcoin doesn't have a central authority in control of its supply (unlike Fiat). Bitcoin's future price will depend on how well it's adopted in the mainstream world. If it ever hits $1m, I'm sure many early adopters like you and me will become filthy rich. Such a high price will also attract the likes of everyday people by encouraging them to buy and "hodl" Bitcoin for the long term.
Whatever you do after Bitcoin hits $1m in the future, it's your decision. You can either sell your coins for cash or continue "hodling" it for the long term. It would be wise to sell a portion of your Bitcoin holdings to help secure your profits. You'll never know when Bitcoin will go down in price again, due to its volatile nature. Just my thoughts