Yes OP, I think rather than asking, “How much should your DH earn.., “ in order to allow you to leave work, the question you need to ask is, “How much do we need in assets...?”
Obviously any FH salary is precarious and if he leaves, he takes it with him.
Having a £200k salary is meaningless anyway because it’s all relative to outgoings. It depends where you live and you haven’t told us this, so sorry if I’m presuming, but if you’re in London, this amount wouldn’t go far necessarily if you have a large mortgage and school fees.
So you have to look at it like this - “If it all ended tomorrow (heaven forbid), would the assets we have accrued as a family in both our names mean that the DC and I would not need to struggle?” For instance, if you’re house is worth £5 million and all paid off, chances are you’ll be ok. But if you live there hoisted by a massive mortgage and / or have other debts, it could obviously be a total nightmare and his salary will solve that.
So protect your children. Look at the whole picture, not just his salary in the here and now. What assets do you have as a couple? What investments / property etc? How liquid are these assets potentially? If you think you have enough wealth as a family, then it’s probably ok to consider SAH. But also, weigh up how easy your industry would be to get back into if need be. Would you even want to? Or would you want to change direction anyway? All things to weigh up imo.