all things has a time to die
I have had these plants and I will tell you after buying them and taking very good care in water or soil about 4-6 years are their life span. I know I have been a grower of them before they even got popular.
I also noticed the curly ones will die faster due to the turning of the stalk before you receive them when the nursery has to get the twirl in the stem. So to say it sadly all things has to die but you can save the top and root from the dyeing plant.
hope this helps no one really will tell people this, A lot just don't know the life span.