I think as long as the heat erasable pens are designed for fabric, the marks won't come back - at least none of mine ever did and I tested them to be sure. And they are the cheap, cheap versions.
The horror stories I've heard, however, are from the Frixion pens, because they were not originally designed for fabric, but paper. I did test those out and to my horror, the marks did come back, so I don't bring a Frixion pen near my work.
My thing is, unless it specifically states that it's designed for fabric, I'll have no issues using them. But, if they were designed for something else, like paper, you wouldn't be able to pay me enough to take that chance. I'd rather be safe than sorry.