I have ten 4x4 raised beds in my garden. Last year, following the killing frost (which didn't manage to kill my kale), I didn't do anything. I just let everything wither. In the spring, it required serious labor to get rid of all the grass and weeds that had grown in the beds.
This year I'm trying a different approach. After hoeing the beds, I'm collecting leaves from nearby trees and spreading them on top of the bed. I then cover the leaves with the uncomposted remnants of my open-air compost(*) mainly to hold down the leaves.
(*) Fancy word for a semi-contained pile of yard waste.
I could see the following things going wrong with this approach:
The leaves will turn into mush and block off any water.
Composting all that carbon will take out nitrogen from the ground.
Some leaves kill subsequent growth. These leaves look like maple (not an expert) and I don't think this will be the case
Remedies
I pick out red wigglers from the worm compost and toss some in each bed to make a last stand.
I'm thinking of adding some blood meal (nitrogen) on top.
Whatever doesn't compost down, I'll throw into next year's open-air compost.
I have done similar in the past, but I just put leaves down. They ended up blowing away. I then worked them into the beds and it worked well.
Leaves are mostly good for improving soil tilth. Not much nutrition at all. When it's broken down it's called leaf mold and is very fine textured. Maple leaves break down pretty quickly. Oak leaves take several years even if you break them up. I use them for mulch in the chicken run and even they can't break em down.
For blocking weeds, what you did should work well as long as it's 3-5 inches thick.
In my experience, putting down a thick layer of whole leaves will just end up having basically the same effect as tossing a wool blanket over the bed. They won't decompose much, but they will keep the bed relatively free of invasive grass and weeds. Come spring, you will have to remove the stiff, sodden lump in order to allow the bed to warm up for planting. One of my new gardening mantras is "Seed is cheap. Food is moderately priced. My labor is expensive.", so what I might do in your circumstance is just attempt a ridiculously late or idiotically early over-planting of anything and everything, and maybe haphazardly throw some plastic over some of the beds. OTOH, one advantage of living at a latitude where beds do freeze solid is that the cold also kills off some pests and diseases you want to die.
Put the leaves on a tarp. Drop a lawnmower on to the pile to break them up into bits. Take the leaf bits and pour them on the beds. Regularly pour human urine on the leaves in the beds.
The leaf bits make a good mulch and the nitrogen in the urine helps break them down. If you mow them up enough into small pieces, they can be mixed in with the soil in the spring.
We have those maple leaves that take forever to break down. Space can be an issue with this technique, but store the maple leaves for two years in plastic waste bags so they breakdown, then mulch with them. I just put a few bags in my basement and forgot about them. Don't forget to soak them before bagging, and tear a few small holes to keep the air circulating to aid decomposition. They works great as a mulch after a year or two and because they are broken down, they don't catch the wind and blow away as easily.