Will these wired keyboards destroy the tristar on an iPad 6th gen?

It’s always possible with non certified accessories. The problem is that they require power from the device and if they don’t have built-in protection circuitry, they can expose the iPad to high power requests and damage the logic board. Like anything else, it’s a numbers game and the probability that any one keyboard damages a Tristar IC is low but when you scale it up, you see problems.

IMHO, from a school district perspective, they should not be allowing non MFi-certified accessories being connected to school owned iPads. With the high number of devices, they will see problems…eventually.