Though, as you said, happily that is changing.
(Edit to say, speaking as a certified ketobro, I don't think you should do keto all the time, forever. A break day or two every few weeks, and stretches of healthy mixed-diet eating, in my experience, gets you the same benefits)
Not just healthy, but essential. You need a certain amount of fats for your sex hormones to actually work, so unless you want to stop menstruating/not interested in having erections, keep eating healthy fats.
furthermore, we have sensors in our body to inhibit sugar craving in the presence of glucose or sucrose. we have no such sensor for fructose. so even if you did have 50% pure fructose in cane sugar, you would drink less real sugar coke because you'd feel satisfied after drinking a much smaller amount than those HFCS abominations.
Sudden jump off keto may cause inflammatory damage to the endothelium of your blood vessels, and while in that one study, effects had been “transient”, I wouldn’t risk cheat days without a very gradual reintroduction of carbs, and surely not repeated cheat days. (My personal fat diabetic ass says it had a lifetime of carbs, though, so that’s not happening for me until at least 20 kg later.)
I know it’s just one study, but I would rather be safe than sorry until we know more. Case in point: the study subjects were all young and healthy, and most people who really need to go very low carb are not.
So a 'cheat day' should probably be more like eating some wholegrain bread, lentils, some raw fruit of choice, or stuff like that. If you're on keto, that will almost feel like eating candy anyway :)