AMG, we had a similar crisis 10 years ago. My better half was found to have 98 percent blockage..
Fortunately, they caught it before a heart attack and stents opened the arteries. He also is a skinny guy who exercised regularly. It's entirely hereditary in his case. Medication is a must to keep his arteries clear--diet alone won't help a case like this.
He lost a lot of weight recovering from the surgery and never really gained it all back. When he was able to exercise again that helped, and he also used protein drinks. They had to be a letdown after years of camembert dunked in hot chocolate.
I have a prejudice against anything fake--remember how they used to tell us margarine and Crisco were good for us? They turned out to be lethal, and I'm wary of other imitation foods--just my own opinion. I also find these products depressing. They remind you that you can't have the real thing.
We switched from butter to olive oil for most things. Avocados and nuts are good for you. Learning to enjoy whole grains and legumes, along with lots of fruits and vegetables will benefit everyone.
I can't imagine that an occasional pat of butter on an ear of corn wouldn't be allowed.
Long walks, when he's up to it, may be the best single thing you both can do.
What a scare. Take care!