did you have the watchdog application installed and setup? If your Pi restarted it should have reset all its GPIO which would have closed your valves.
Wont work on current board but mebe for future ones we can use the RTC w/a hardware timer to cut power to the stations when triggered, then anytime a watering program goes off we set that timer to either a big default or the time the program is supposed to conclude; then if anything prevents the microcontroller from completing the program the RTC will be a failsafe to shutdown the stations.
And yeah email alerts could be used for alot of that; but lets just say internet is down/unavailable… or were using it to close the garage door in which case it would be to alert anyone who’s in the garage that the door is about to close.