C16 PLAs are much more reliable than their (Breadbin) C64 counterparts, but they aren't immune from failures either. I am confident that the lower temperature that we will obtain inside the case with LittleSixteen will help them survive longer - if not ever - but in the worst case full official documentation of the inner workings of the PLA is available in some leaked C16 manuals, so we are able to make an accurate replacement.
Someone already did, actually, and that is Daniël Mantione with his PLA16V8 project, which reimplements the C16 PLA with a GAL16V8 and a few extra components. Daniël managed to squeeze all of this on a small PCB in the same size and pinout of the original PLA in order to make a drop-in replacement, but since we can modify thing at will I integrated the adapter into LittleSixteen. The GAL16V8 can be plugged in a smaller socket that lies underneath the standard PLA socket:
The extra components (6 diodes and a resistor implementing a 6-input AND gate) have been placed in the empty area right of the modulator:
Of course these components are not supposed to be mounted when an original PLA is used, but I think they won't hurt in any case.