Medical Cost $50,000 Deductible was $5,000 then 20% coinsurance. Out of pocket is $6,000 So he paid $5,000, then $1,000 coinsurance. Then they paid 80% of the bill $40,000. So he would still have to pay $10,000
Is this the way it works?

So his cost would be $,5000+$1,000+ $10,000

Not enough info on plan payments really,

At what point ( if any) does it go to 100 percent payment, normally there is a max out of pocket, before it pays 100 percent.

If not, yes that is about it, it is a trade off for lower prices of health insurance payments.
Many people today carry a 10,000 dollar deductable so they pay the first 10,000 before insurance pays anything.

Our plan here, we pay 1000 deductable they pay 80 percent and we pay 20 percent of rest

Thanks a million. There is no free lunch.