To answer your actual question -- it depends. Cheaper motors will be more susceptible to high temperatures, better motors will withstand them better.
The two top contenders are probably the windings getting hot enough that the insulation fails, and the outer bell getting hot and the glue holding the magnets on fails. Both of these depend on the manufacturer, basically on what materials they used and, hence, what price vs. quality compromise they decided to make.
AFAIK, if you land and the outer bell is lower than about 80C you're fine for even cheap motors, and ditto 120C for the windings. But -- I dunno, and I'm always getting surprised by just how cheap of cheap crap gets unloaded on unsuspecting modelers. If it's a name brand motor and they're making promises about temperatures, I'd believe them more -- but only more, not absolutely.