Why is my RF switch catching on fire?
I ended up adding 620 ohm series resistors on my +/-15V traces going to the chip (power and enable pins) and that fixed it. The device draws next to no bias current. 

My thought process was inrush current causing a burnout of the internal protection diodes, leading to shorting. 

So, with the absolute maximum digital current of 30mA in mind, I chose 620R, because 15V/620R &lt;30mA, and wasn't large enough to cause huge RC time constants which could add its own issues. This prevented further killing of switches.

In retrospect, Im not sure if the problem was inrush current -  Selvek was right in his comment on voltage overshoots, as my cable is over 10 feet! Lots of inductance in such a cable; energy is stored in the magnetic field, which gets released when plugged in - causing a large transient voltage overshoot at the sensitive switch. Adding series resistance just damped this overshoot to acceptable levels.