I planted two pineapples a few months ago. One is thriving and the other is barely surviving. Should I wait and see if it rebounds or just mulch it?
The second photo looks like a healthy plant that got eaten by an animal or run over with a lawn mower, not like a plant with a disease: purely mechanical damage of an otherwise healthy plant.
I'd just let it be and see if it has enough energy stored in the roots and enough remaining leaf mass to grow back - the worst thing to happen is that it doesn't.
If, on the other hand, you had some kind of infection (which you don't), I'd recommend removing it to protect the other plant.