PAL chips are programmable, so you would need to have its copy... (AFAIK)

Odds are the PAL would be an optional component that only needs to be fitted if you're using the Weitek co-processor socket. Probably just a bit of cheeky cost-cutting, given that the majority of users wouldn't need it. I doubt it's the reason your board won't boot.

I'd suggest doing all the standard troubleshooting first: check all the voltage rails for correct voltages, check the rails for shorts from bad tantalums, pull the BIOS ROM and clean all the contacts and re-seat it, confirm all the jumpers are set correctly, et cetera...

If that doesn't do the trick, then unfortunately you may have to try and figure out what logic function the PAL 16L8 was being used for. Pins 1-9 and pin 11 are inputs, pins 12 and 19 are outputs, and pins 13-18 are bidirectional I/O. (Pin 10 is GND and pin 20 is VCC.) If you can trace what the input/output pins are hooked up to, we can probably figure out what the PAL was meant to be doing. They're pretty simple devices, especially the 16L8 which doesn't have any flip-flops or registers inside it. Again, I think that it's most likely handling the address decoding and chip selects for the Weitek socket.

What's the mainboard company?