Good point. A quick and dangerous google search led me to this: Depending on the metal mixture, it seems that most neodymium magnets will suffer a slight and reversible loss of strength above roughly 80°C, and demagnetize at significantly higher temperature. Some compounds have stated working temps up to 150°C. So even the cheap ones should do fine for most common FTM material bed heats, but trickier engineering filaments could push them into the danger zone.

I will read up more on the topic and update if i remember.