@pearsonhenry2
Yes – “If the Pi drops off the WiFi it can’t then tell you is isn’t on the network”.
An alternative (which I use) could be to run a script (daily?) that sends you an email with the message eg: “ALL OK – I’m online”. Then if you don’t receive the daily email you know something is amiss.
It appears that you are concerned about feeds to emoncms.org not happening.
If emoncms.org is used solely for backup reasons then having a local backup would side step the loss of WiFi issue.
The local backup would be to the SDHC but it could also be copied to a USB flash drive as an added protection:
Going further (as I do) it is possible to have a second Raspberry Pi on the local network (hardwired) that receives the data from the first RPi. This adds a further level of backup protection.
Also I can envisage a script (using nmap?) running on the second RPi that periodically checks for the WiFi connected first RPi and sends an email if it’s not found on the network.
By sheer coincidence, I’ve recently posted to a thread re: sending emails:
Hope some of this may help