I doubt that the crystal can be damaged by using the radio with a retracted antenna, but the transistors in the power amplifier may be damaged by overheating. When transmitting with a retracted antenna the RF-power which should be emitted by the antenna is instead converted to heat.
The power output of our radio sets is of the order of 1 W. The heat produced by such a small power is easily dissipated by even a fairly small heatsink. IMHO it's plain bad design if radio sets can't handle a power on, retracted antenna situation.

As far as I know there is no reason why a synthesised module should be more sensitive to heat damage than a plain old crystal module.

/Red B.