Hmm. So, if we purchase a Microsoft Surface or maybe a MacBook, these devices combine hardware and software into one device. In that situation, it would be much harder to switch to Debian for example, and as such the only way to keep the thing running would most likely be through official support of the people you buy it from. They also make you agree to a long license agreement in order to use the device.
The Purism devices don’t have that kind of license agreement, I think because they are styled after a different manner of thinking and a different audience. The hardware and the software are more able to be separate. You can switch to Debian if you want – I would imagine with no impact on any warranties, etc, because the hardware is getting considered separate from the software. You won’t find an annual fee on PureOS like how Microsoft prefers to sell licenses to things that periodically expire.
So, while this means that Purism I’m guessing would only really want to help you with hardware issues and not software issues, it also creates a problem for you because I would imagine Debian would not solve your problem at all, would it? What’s your financial relationship to Debian that they would give you tech support?
If you want enterprise software technical support, maybe you could try installing Windows or Red Hat on your Librem Mini device. I’m not familiar with that, but I believe some of those corporate systems wherein you would pay money for access to the software probably also would be more likely to give you tech support. Seems to me like that’s a little like selling your soul, since it might tie you into a financial relationship from which you might never feel free to escape. But, that’s one way to get the type of technical support you apparently desire. [If I were a betting man, Red Hat would be more likely to work on a Librem Mini, but I haven’t tried either one.]
Purism devices try to offer freedom; so, you’re free to try to put Windows or Red Hat on there and get some software tech support that way if you want. It’s probably a bad idea, but you can.
And, in such a case that you buy some proprietary software that includes tech support to power your device, Purism as a hardware vendor would continue to offer hardware support but probably won’t want to offer you software support, I would imagine.
tl;dr PureOS literally repackages the software from Debian so if you change to Debian what are you even expecting to be different?
Edit: see information posted by others below, some of the information I posted is not correct