Just tried that and realized that ifup/ifdown commands have been obsoleted and do not work.
Here is an updated /usr/local/bin/wifi_rebooter.sh
# The IP for the server you wish to ping. I ...
No it won't work.
It will certainly stop the Pi BUT unless you do an orderly shutdown you risk corrupting the FS.
The RUN pin should really be labeled RESET (with a bar - indicating active LOW).
If you want to shutdown a Pi (regardless of whether it uses SD Card or HD) you should run poweroff which enables a controlled shutdown, flushing buffers etc.
If you do not do this you risk corruption ...