Protecting MAX485 data or supply from shorting to 24v DC supply
The micro will surely be destroyed. You can prevent it by either preventing the short in the first place or by adding series or shunt protection. For example,  you could add an LDO regulator on each board that is capable of withstanding 24VDC on the input (series protection). 
Most RS-485 protection schemes are designed to handle transients, not a direct short to something like 24V so you would probably destroy a shunt protection device (typically a TVS array is used) if you add a series polyfuse type PTC or MOSFET based current limiter you can make a short to +24 survivable.