I'm wondering if this can be done with Simple Lighting...
If a light switch is on, ignore the motion sensor, else turn on switch if sensor == active, and disable switch if sensor == inactive.
I thought this would be possible with simple lighting by creating a rule that turned on a switch on motion active, and turning it off when inactive, and then adding the switch in question as a restriction... but, all that seems to do is disable the motion sensor after the light is on.
Do I have to delve into the rule machine to get this behavior, or is there a way to do it with simple lighting?
It sounds like you want the light to remain on, if it was turned on manually, rather than auto-on/off via a motion sensor. In that case, you can look at "Motion Lighting" app, using the "Don't turn off, if already on" restriction.
Make sure you do not select the switch under "Switches to turn on". This will trigger the motion lighting app not just turn the switch on. That will supersede the setting for "Don't turn off if already on.
One thing to note. If the switch is within the motion sensor's field, this implementation will not work because motion will always turn the switch on first. This only works if the switch is outside of the motion sensor's detection area.