I really don’t think bricking is likely at all here. How you handle this depends on your use case. Here’s what I’d do based on the limited info I have on your application.
Easiest option:
If you plan to recover a device and charge it manually before redeploying, you might just want to hit the reset button after charging so that starts at the very top of your firmware, recognizing that it’s now back above 20%, and chugs along as intended till it gets back to < 20%.
Only slightly more challenging:
Jumper VUSB to WKP. When you recharge using a USB cable, it will then trip WKP (5V tolerant) to come out of SLEEP_MODE_DEEP and start from the top. Though if it makes it through to the SoC check logic and it’s still under 20%, you’ll have to do the first option after you charge it for a bit anyway so this is only advantageous if you can’t access the RESET pin/button for some reason.
A little more detail on sleep modes here (and in the docs, of course): Electron SLEEP_MODE_DEEP tips and examples.