By the time you pay someone for custom cabinetry you are going to be spending quite a bit, not to mention the significantly smaller interior space of the counter depth refrigerator. Is your family downsizing or do you have a refrigerator. in the garage? But I feel your pain having just bought another sub zero.... which I love. But they are $$$$, I did no custom panels this time which cut down on the cost a bit. My last one lasted 25 years!

That's 42 wide? May as well replace with Sub Zero. Or live with the hack job and jury rig that in the end, will cost as much.

I do not agree tha a sub zero ber is the answer IMO a totally over priced item and get a new fridge you like in a counter depth 36” wide and have a cabinet maker do his magic but there will be an issue with matching those cabinets perfectly .BTW counter depth fidges do not waste space you lose 10% of the storage and honestly finding stuff in the fridge is just a lot easier. I run a catering biz with a 32" counter depth fridge no issues . Remember the new fridge will need breathing space around it so the look will be a bit different but IMO a lot less money than 8-10K

Built ins are done for a reason. It will cost about the same, no matter what route you take. If you have to drop down to a counter depth and go cabinet depth , that will cost as much as a built in . You’re not matching those old cabinets very easily. You need a very experienced custom cabinet maker. It’s also an obvious downgrade to the level of the kitchen. If you can’t replace like with like, that’s a big red flag that you may be in the wrong house for you.

Much as I agree about spending $8-10K on a fridge, if I were you I'd bite the bullet and find a way to purchase another built-in. With the nature of the adjacent cabinetry it seems like anything else will degrade the overall appearance of your kitchen which looks very nice by the way. We have a 20 year old built-in subz that came with the house. So far so good but I've built myself up for the fact I may have to replace it with another one some day.

A standard counter depth refrigerator in a built in’s spot just looks wrong. It also sends a message that other things in the house maybe were not kept up or maintained to the home’s original high level. Maybe you do a “garage fridge” type something now, just to get cold food. But plan to replace it properly, with the built in, later.

We had a 42" SubZero with a freezer on the bottom that we think was original to the house (1984). It finally died a couple of years ago, but we knew we were going to do a big kitchen remodel in a few years, so we didn't want to buy another built-in without knowing what the remodel would be. So we bought a 36" side-by-side counter-depth KitchenAid. It's been OK but is not big enough for our family of four, and the ice maker just broke, of course out of warranty. I had to have our fridge wall reconfigured to accommodate the smaller fridge. We also bought a regular depth one for the garage. So about $6,000 for fridge plus carpenters to build open shelving (not nice cabinets) around the fridge, plus another $2000 for the garage fridge. But now we're embarking on the remodel and I've been researching 42" refrigerators. Once you go larger than 36" the price jumps a lot. I wish we had just bought the nice SubZero a couple of years ago and worked it into our remodel. They last a long time and do a good job. So my point is that if you're going to be in your house a while, I think it's worth it to get the SubZero. Plus if you already have a paneled fridge, it might be a downgrade to your kitchen to not have a built-in? I realize it's a large chunk of money though. For our remodel, the fridge is our "nice" appliance and we're going mid range for everything else.

I wouldn’t try to replace a built in with a counter depth, like someone said. It will never have the appearance of a custom built in. Also counter depth refrigerators are very shallow inside because they have the compressor in the back. The sub-zeros (+ some other brands of built-ins) are designed with the compressor on the top, that’s why they are taller and deep despite not sticking out.

You said your Subzero is having problems. You can find out the age and exact model # on the manufacturer info label printed on the inside of the door. Mine was located inside the freezer, other models in the fridge part. Label inside looks like this (not mine):

Yours looks old, might be near the end or might be fixable.

New stainless panels to replace the dated wood panels goes a long way on an old-but-functioning Subzero. Here’s a 42” one from 2006 with a new panel kit from last year for a house, it was an easy change vs getting a new refrigerator.

There is also a 2nd hand market for used Subzero refrigerators from luxury homes getting new kitchens and the latest model appliances, many have these wood panels that come right off.

I think you could use a Fisher Paykel integrated fridge and then have fillers made to make up the width and height difference. Get the SS doors.
The fridge is about 4K and then another 1-2k in carpentry. It’s totally doable and with the right trim carpenter would look very intentional and high-end.