You should see a green banner advising when connectivity to your device has been lost (such as when it has run out of battery). Press the ? button on the banner and SkyDemon will offer to switch back to your internal GPS until your traffic receiver wakes up again.

Thanks Tim, for taking the time to post in this thread. I understand your position; but given that I remain under obligation to use mark I eyeball to avoid other aircraft when VFR, I am  likely to discontinue using PilotAware with SkyDemon. SkyDemon is vital navigation/ infringement avoidance software for the whole UK GA community, and I would rather maintain its continuity than see a couple of extra bits of traffic on my screen. Put simply, if I have to choose I'd rather use a GPS source in an instrument (iPad) with an installed base of 10s of millions, and a demonstrable reliability in service, than a power-hungry niche Raspberry pi setup that does a reasonable job. I still think it's a reasonable suggestion that users can choose their GPS source and traffic source independently.