What happens if there's a network interruption during a Radmind update session? (Power outage, ethernet gets pulled out, whatever.)

Only lapply actually changes the filesystem. It has a tri-valued exit status. 0 means that everything is correct, 2 means that an error occurred, but the filesystem was not modified, and 1 means that an error occurred and the filesystem was modified. This allows a script that calls lapply (e.g. a logout hook) to retry, waiting for whatever the problem was to be corrected.

In the event of a power outage, it is possible though unlikely that radmind will leave the machine in an unbootable state. lapply guards against this possibility by first transferring the file over the network, and then installing it. However, if a kernel upgrade were in progress, and the kernel itself were upgraded, but the various kernel extensions were not yet upgraded when power failed, the machine may not boot. This is very similar to problems that can occur during normal system upgrades and are corrected similarly.