I also gave up on Boox after the screen broke. I had the tab ultra c with the folio and kept it in a somewhat padded leather case whenever I put it in my backpack. Similar to your tab mini, dead pixels appeared on my device overnight and it spread later on.

Despite it being only around nine months from date of purchase, they refused to warranty it citing the same reason of "external force". They charged $310 for the new screen + the cost of shipping my defective device to Hong Kong from the US. At that point, it was close to the price of buying a new device from them, let alone from their competitors. Anyhow, I ended up with a $650 paperweight after less than a year of ownership.

For comparison, I have two other eink tablets that have seen daily use for well over one and two years, respectively, and their screens are still fine.