So, my DSE has overheated...

As per the title, my DSE overheated coming out of the highway. Was cruising normaly at around 130km/h and noticed that the temperature needle was a bit over 12h. Stopped at the tollbooth and it started to rise, rise and eventually went into the red and the warning light came up. Stopped immediately on the curb, stopped the engine and let it cool down. Upon further inspection I noticed that the fan was not locking. At that temperature (very high) I could freely rotate the fan by hand, so I'm guessing that's where the problem lies.

Now, I'm sitting here, 100km away from my favorite vehicle (mind you, I love my Series 3 just as well, but they're sitting side by side now so they're both 100km away from me), obsessing if I should be worried about having burned the head gasket. I'm 100% sure that the overheating was caused by the fan but could this have resulted in HG failure ?
After replacing the fan, what could I look for just to be sure that the HG is intact ?

have a look in your expansion tank, if there are air bubbles coming in from the return pipe your in trouble. hate to say it but i found the same thing. if you ignore it after you change the fan your guaranteed to blow a few radiators to find the truth. if unsure get a pressure test done. i had to fit a new engine to mine after i found the same thing..........

good luck you might be ok

One short overheat and you may be OK especially as the overheat was at idle when the engine was not stressed.
Perhaps you should consider fitting the mod to use the aircon fans either as a back up or replacement for the viscous fan.