Yes, I'd appreciate if we can move past this part of the discussion since it really is only tangentially related to my decisions. He isn't trading futures/option nor did I say all of his investing is in the stock market (nor is it crypto which I am sure people are thinking) nor did I say he is risking $300K...I was only explaining that we have a portion of our assets in cash for this reason since most mustachians would consider it silly if there was no use for it than parking it in an account early 0% interest.
50% of our cash assets are mine and 50% are his. He will never be able to ruin what I have saved. Given that, does it help frame this possible downside risk any better?
You have ~$656K of investment assets: ~$26K of spending at 4% Rule
you have rentals throwing off $60K : ~$60K of spending
you have 5 years of expenses (and 17% of your properties' value) in cash so i fell no need to haircut your rental cash flow to account for repairs or something and you seem like you'd be a perfectly capable real estate investor and probably already are doing so.
With NEITHER of you working, you all are more or less financially independent (maybe not quite w/ healthcare but probably pretty damn close).
If your hubby made $40K from a boring w-2 job (20-40% of what he makes), you'd be very financially independent even if you make $0 working for the start-up. If he can sustainable make ~$100K, you all are extremely financially independent.
Absent any disasters with your real estate holdings or your husband's trading operation you are totally fine to retire or take career risk (which you acknowledge isn't really career risk since you're super awesome at your job and could always go back).
So to me, the thing to do is to be overly prudent with mitigating your legal risk from being a landlord (and evaluate your concentration in whatever market you're in and risks to said market), to be sure you've done a bang up job in accounting for all contingencies wrt the real estate, and to make sure your husband doesn't blow up in doing whatever he's doing to make a consistent very high ROE on his bankroll.
You're going to be amazingly fine in 90-99% of scenarios. So guarding against the 1-10% is all you've got to do. Whether that's from a tenant landlord lawsuit going awry or an October 1987/2008 volatility event (or the equivalent in whatever he's trading), or your city's rents/property values declining, that's all you have to worry about.
to me, you're asking whether you can leave the security of "big tech". The answer is a resounding yes because you have the security of a) cash flowing real estate portfolio b) investment nut c) hubby's trading acumen.
So as long as a, b, and c are good (really as long as 2 of them don't go bad at the same time), you can leave the security of big tech very easily. So I'd be most focused on things like
"do i live in a recourse state"
"have i personally guaranteed all these mortgages"
" have a set up a separate management company that does all the property management"*
"is my market dependent on any one company/industry/whatever or are expenses likely to spike in some material way (for example property taxes if you live in chicago or connecticut which some say are the next puerto rico)...
"can I set up some kind of LLC for hubby's trading operation to shield other assets in the 0.1%, 0.5% 1% probability scenario"
"will losing the security of my income at all effect the way hubby trades"
In short, you're totally fine to do whatever you want as long as your assumptions are correct.
*note: I'm not sure if this actually does anything and would defer to people more experienced in legal liability risk mitigation / asset protection / whatever you call it