First I went back to the previous diet. But keto “worked”, I just missed my vegetables. It was a pretty nice low-carb diet without processed stuff and almost no lactose, grains and legumes. I felt right there. So I had it easy.
When I went low-carb, there was no way back at all, just forward.
Now that I do carnivore, I still can (and will) go back to keto but it can’t be the same as before, I changed too much.
I always do this, keep something I like (even if it’s a negative keeping so I keep avoiding things), change things that may need it, add things I missed or find useful… And we will see. I jump back too if it amuses me (or can’t resist). I just come back, usually very soon and don’t go way too far for long.
I don’t worry, I do what I can and my body handles the things it must. It’s not probable that someone will force me to eat high-carb or low-fat (or worst of all, both at the same time), ever, for longer that I can handle well enough.
I always have options.