I have a 2001 Honda Accord and I'm changing the oil pressure switch / sensor. The terminal cover crumbled apart when I took it off. I couldn't find a replacement part for it, so is there some way to fix it? Could I just leave it as is? Also, the switch is very difficult to access, so I can't simply wrap it with electrical tape.
If the connector is still intact and can attach to the sensor, just plug it in. If you want to remove the outer "protection" (what's left of it), then remove it. It should not affect how it works or functions. The major part here is a good electrical connection to the tip of the sensor. If there is heat present, put a small amount of heat shield tape on the tip to replace the part you took off. Do this before reconnecting it. The only thing I see there in the second photo is there seems to be a coolant pipe running very close to it. If that is the only real heat source, you shouldn't have a problem with heat, as that doesn't get too hot. It shouldn't melt or affect the wiring.
Assuming that Honda no longer offers this part, you might check the usual places for NOS service parts like EBAY. You might also check for used parts at used part suppliers or local auto recycling centers (a.k.a. junkyards).
If that fails you may be able to fashion a reasonable facsimile out of some silicone compound and an epoxy like JB Weld.
Worst case, wrap it in some electrical tape. It may be somewhat difficult to access but if you remove some of the things in the way it may be easier.