Nothing stops Murphy from knocking. What matters is to keep his old but from entering. Taking care of the low hanging fruits first puts up a get front.
P.S. Many other chips have multiple Vdd and Vss, I using only one of each because I stopped Murphy from even getting out the bed baby.
Don't do it, bad plan. The internal interconnects are very tiny wires, to be reliable you need to hook up both VSS & VDD pins. Of course you didn't skimp on the decoupling caps...
Anybody want to pic a multiple Vdd/Vss PIC and run a reliability test based on using only 1 Vdd and Vss? Draw a matrix of usages and results, then return with hard statistics that can be varified by third party using said matrix. if not, anything else is vapor.
I would have expected the designers at microchip to have taken advantage of using the 'extra power' pins for some other other PIC function,
if they had considered a dual set of power pins wasnt required.
The PIC designers allocated them as power lines for a reason, so I would recommend you use them.
Many ic's work outside their design parameters, for MOST of the time, if the reliability of the project is important,
stay within the devices design criteria