Hi,
New here, but may be able to contribute something.
HF Antenna: The state of this would be reflected in the vswr reading, which essentially says how well the transmitter is matched to the antenna. If the antenna is missing, or cable open circuit or shorted, the transmitter autotune would detect it and either run at reduced power or shutdown completely.
Whether this would result in an ACARS message, someone else may know, but it is detectable and should be logged...
Regards,
Chris