Here's some barely-better-than-napkin math on how long $5 Million will last you if that's your only income: YMMV depending on where you live (state taxes) and your investment strategy or risk tolerance.
You just made $5,000,000. Awesome! Now, depending where you live, capital gains and income taxes make about 35% of that go away.
You're now down to $ 3.25 Million, nothing to sneeze at.
Next, we need to invest it fairly conservatively, in dividend-distributing vehicles. Let's call the return $6% annual. So now you're making $195K just for enjoying life and watching the grass grow.
However, you need to account for future cost-of-living increases. Generally speaking, we're told to expect a 3% cost of living increase.. so you need to fund half of that 6% investment into your investment principal.
...So that $5 Million windfall should give you the equivalent of about $100,000 per year for the rest of your life, if you manage it wisely.
As to whether or that is "enough" - many factors come into play. $100K per year is not enough to support a family and home ownership in many parts of the country and I would recommend some level of prudence.
As to the original question.. my advice for the entrepreneur? Take the "bird in the hand", invest the $5 million as laid out above, and consider any job you take (or starting another company) as always having a $100K per year kicker. Certainly enough to boost you to retirement much earlier than without...