Yeah, I'm not sure either. Out of curiosity, which firmware revision is on your switch?
Asking because when I first got my 9024D-M switch (running firmware v0.8.6) and took out the fan, I'm "pretty sure" it got hot fairly quickly. At which point I put the fan back in.
However, after reading on the ServeTheHome forums about other people running the exact same model switches with the fan's permanently out... I decided to try again:
http://forums.servethehome.com/networking/1595-voiltaire-4036-noise.html#post15194
This time though, the firmware had been upgraded to v1.0.5. The switch hasn't gone over 55 degrees Celsius since, so I'm just going to leave it running fanless now.
Suspecting the newer firmware version had an influence on the heat of the switch... but I could be imagining it.
You should be ok to run yours fanless... but yeah, you'd want to find out for sure what happens if it gets too hot.
You could rig a remote power off switch up to a themometer type of thing if you're feeling adventurous...