OP it sounds like you don't have enough money coming into the household for him to be a "kept" man. Unless he has a £2million pension pot he can get his sticky paws on in 5 years time and savings to last until then.
And by kept man I mean having a cleaner, home help and gardener.
Who doesn't want to retire at 50, not do any household chores or childcare and "just potter and hobbies". Really who doesn't want this?
But real life isn't like this.
So insurance money aside. What's his plan? He understands that his decision affects your children as well. You say he is a good dad so start from there.
You children are at ages where shortly they will be looking towards starting out in adult life, uni costs, car, apprenticeship? To help them on their way does he understand they will need a bit of cash.
Maybe a holiday for the kids would help.
My H, when I fell pregnant we thrashed out the details, took on the financial responsibility.
He worked full time, 60+ hours in a stressful job. It ground him down sometimes, and I fully supported him as I could but the kids need a house, food, fun, an education.
With full support he kept going. He now has a job just as intensive but his hard work is now paying off for him, as for all of us.l
My H is a "good dad". How I see it. He works like a dog with grace, he wants to provide, he talks through homework, takes them to sport hobbies, when they were younger they went to the park, he talks to them, teaches them, plays with them, provides, protects and encourages
"Enjoying sitting on a sofa watching a film" is just not enough to be a good dad. Sorry.
So you need to both, as adults juggling a lot of balls, sit down and have a mid-life thrash out. How are you going to work together with everything that you need to do going forward?
You need to firmly, in a kind way, explain that retirement to potter and hobby around is just not an option right now so he needs to forget that nonsense and work out something else. Whether that is perhaps changing his medication to get him back to work or just more enthusiasm about life, you earn more but he takes up more house, a different less stressful job but if you work more the household and children need a more equal split.
Explain if you are working and doing all household and children that in time your relationship will not survive, you will feel resentful and everything you have built up will be lost. He really needs to understand this.
He can't check out of life and be a pampered prince from now until the end of time. He doesn't sound dumb but he needs to take ownership of the real life long term consequences for him, you, your children, house, future, pensions, retirement, health, of his decisions.
I hope you can find a solution going forward together.