I would think that as long as the chemicals making up the ink of these pens is still on/in the fabric, there is a big chance that, one day, they will return to a visable state. If I were to use the pen, I would be sure to wash it thoroughly when completed.
You would think that by ironing it, the ink would be heat set. I'm not a fan of using any kind of pen on quilts. Several of the inmates were using ballpoint pens to mark around their templates & spilled something on the quilt. When they went to try to wash out the liquid, the pen bled all over, creating a giant mess. They have been ordered not to use pens to make a quilt!