Chardy
In the 80s, I lived next door to a lovely couple. He had a bad heart plus all sorts of other problems, but looked healthy if very easily tired. She totally did everything for him. They had a plan for what she'd do when he died. One day she dropped dead. He had no idea how to look after himself, shopping, cooking, washing clothes, paying bills, cleaning, nothing.
But they were my parents' generation...
This happened to a girl I used to work with. Her parents lived a long way away, her mother fell seriously ill and her father didn't even know how to address an envelope. She had asked him to send her some papers so that she could look at them for him, but they ended up coming back to him!
On the other hand, one of my DH's uncles learned to cook and even bake well into his 70s when his wife became wheelchair-bound.
As to the question in the OP which wasn't about whether she should cook for her DH, but what she could leave for him, it depends on what sort of thing you usually eat.
I agree that he should learn to be a bit more independent but when you are preparing a meal, it's hardly any bother to do an extra portion and freeze it or pop it on a plate and put it in the fridge for the following evening.
Risottos,
anything done in one pot: casseroles, chunky, filling soups.
Mashed potatoes and a slice of cold roast.
Or a shepherd's pie, single portion in a cereal bowl.
A pasty.
Pancakes or waffles that just need reheating in the toaster or in a dry frying pan. Served with ham and/or cheese.
Maybe something you don't like but he does. Mine always cooks himself pasta and douses it in pesto. Two things I'm not really keen on. But pasta is the only thing he can cook.
Oven chips are a simple accompaniment to many dishes.