RRF has some clever settigns which can denote what happens when an endstop is triggered. in the case of the tool-detect switch you can have it turned on and off at different points in the script and also change it's behavior. Depending on how you have it configured you can have the print pause whenever the tool-detect endstop is not in the expected state. I can't remember the exact code, maybe @dc42 can elaborate for us
A tool detection switch is worth the effort. I currently have the switch on the toolhead wired up as a filament sensor. If there is no tool present, the print will pause. In my experience, the tool head detection is more effective to determine 'is there a tool' versus 'is the tool missing'. I think it is due to the way the filament sensor is integrated to the software while 'no tool is currently selected'. Regardless, you can enable tool detection with M591. I enable tool detection as the last line in TpostN.g, then disable it in the first line of TfreeN.g. An example for T3: enable (TpostN.g): disable (TfreeN.g): At the end of the day: if you don't have a tool you likely either missed a step or some sort of interference knocked the extruder out of the parked position. If your print paused due to a dropped tool, I'd recommend re-homing x and y.
Ideally, it'd be awesome if more advanced scripting were possible and you could, for example, rehome C and retrigger the tool pickup macro if tool pickup fails. But yeah, even tying it in place of a filament runout sensor could be useful. I've never had a tool coupling fail in the middle of a print, though.
