As a lithops owner you know how difficult it is to find the best care in the conditions you can provide. It takes time and attention and works only by trial and error. Too hot, too cold, too wet - the plants life and wellbeing depends on the right balance. And still, even if you think you've figured it out, lithops can surprise you, in a positive as well as in a negative way. Sometimes they wither without any warning and sometimes a plant you've almost given up survives and gets better. Here's an example of the latter:
this bunch refused to regenerate for almost two years and now you can say it looks "very interesting" at best. I didn't have much hope for it and yet it's still alive and is pushing up two heads of new leaves!
Its neighbor had the same problem but is a bit further along. Never give up on these guys :)