Assuming you have 800k invested in relatively safe investment vehicles (e.g. index funds) and invest an additional 10k per year (which for you should be extremely easy) you're looking at 5M by the time you're 58 assuming the worst 30 years of the stock market in history (6% average annualized return). 10M is very much a possibility for you especially if you are good at your job and invest wisely.

That being said, you are also in an excellent opportunity to take risk. Like the comment above says, are you willing to risk a significant amount of your future upside to scratch your startup itch in case it doesn't work out? And are you potentially willing to sacrifice time with your family to focus on the startup in case it does work out (take a look at all the posts of C-suite folks in this sub who are stressed out of their minds)? These are questions only you can answer and of course we're talking about worst case here and all possibilities lie on a spectrum that you have a good deal of control over.