What kind of monitoring gear do they use that would not be destroyed by the magma?
A fascinating question and I can only guess.
My guess: when the heat/pressure becomes too much for conventional drilling-—a microwave type that will melt/ vaporize the rock.
to remove the vaporized rock a smaller diameter line will down the bore with compressed gas(?) to cool and blow the spoils to the top. Also, wires for power, signal, and instrumentation will be cooled by the gas.
Still very hot but possible.
With luck, someone that actually knows of this line of work will fill us in.