Hex Decompilers for PIC

Decompilation is unlikely to be a practical solution, and it is even less likely that a tool for your specific compiler and instruction set combination even exists.

Disassembly however is straightforward, though whether you will be able to make sense of the resulting code is a different matter since no comments or symbols are preserved in the HEX file; if you have the original object code it may render the disassembly more readable. There are many PIC disassemblers available, just Google it; I can't direct you at any specific one because there are a number of PIC families with different instruction sets, and you did not specify.

A simple approach to disassembly would be to simply load your HEX file into MPLAB and select View->Disassembly Listing, then right-click the windows and select "Output to File". This output may need some massaging for it to be suitable for input to an assembler.

There is a list of PIC disassemblers at the official PICList technical reference.

Many people never use a stand-alone disassembler, but prefer to use the disassembler inside their favorite PIC simulator.

http://piclist.com/techref/microchip/dissassemblers.htm

http://piclist.com/techref/microchip/simulators.htm