Craig, in my experience a "temperature sensor" and "sending unit" are the same thing, so I'm not sure what you are speaking about.
Temp senders normally are a lot like a squat spark plug in appearance. There's usually only one wire attached, which runs to the guage cluster and then to a 12v positive source. Inside the sender is a thermistor, a blob that changes resistance when the temperature changes, which in turns controls the voltage flowing through the guage, which makes the meter needle move from C to H.
If you break the wire off, just fix it. Solder it, crimp a new fitting on the end of it, put in a foot of new wire if needed. Not at all critical, anything close will still work equally well.
I just looked it up again in the service manual and this is called the Water Temperature Switch. This is in addition to the Temp Sending Unit.
There is a threaded end on the switch that screws into the fresh water pump. On the exposed end there is a wire that connects to it. I busted this wire off, but the way that it was connected is not typical like a ring terminal. It's like the end of the wire was attached by pouring plastic on top of the switch and when it solidified, it was stuck. Maybe I am over thinking this is just a type of soldering that I haven't seen before.
Craig, the wire may have been soldered or crimped on, and the plastic 'cap' added to help secure it against vibration, insulate it, or something else. Unless it was some type of plastic jacketed crimp fitting.
What is left for the wire to be connected to? Any type of stub, post, bit of metal to re-attach it to? If there is, you can probably try to resolder it to whatever metal there is (which may mean scratching out a bit to get the contact area) and then apply some epoxy putty (i.e. plumber's epoxy or JBWeld, more heat resistant) as a new cap over it. How well that will work depends on what you've got left. And whether you can afford to risk it failing in future.