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In terms of visibility, it's wise to have fallbacks. Wear a hi-vis jacket; carry spare batteries for your lights when possible; and check your local laws about wearing lights on your person. You can see when your front light is failing, but your rear light is behind you and probably below your saddle, so it's easy to miss that it's failing until you dismount. Many jurisdictions allow you to have a second rear light clipped to your hi-vis jacket: this gives you a fallback in case the main one fails, and also gives a higher position which can be visible from further. But there's variability: I know that in the UK a body-mounted rear light must be set to flash, but I have vague memories of another country where it had to be non-flashing. You're also going to want to try to fix it to yourself in such a way that it's pointing behind you, rather than up or down, when you're in your primary cycling posture.

My experience is more urban, to get from A to B; I get a hint from the question that you're cycling in rural areas for pleasure, so this second point may not be relevant. In my experience, junctions are the biggest worry for visibility. My penultimate crash was into the side of a car whose driver pulled out of a side-street with only a quick glance for a car's headlights and didn't register my bike's single headlight. In rural areas a single light should be more visible, because it's not lost against the glow of streetlights.