First, again, they are not selling the usb with those recordings, they are selling the guitar, and...
No, you don't need to buy the guitar to get them, there will be other way, kind of...
The first mini guitar, the Gibson, it had an usb with compilation of soundboards of all MK tours where the soundbards were available to purchase. Those compilations are on the MK YouTube account so anyone can listen to them without having to buy the guitar because, it was a bonus, not the product.
I guess they would upload videos like those to the official YouTube channel sometime, so just keep stay tuned to their social media as they announce those videos there.
And don't worry, as you are not missing a thing, we all have those recordings!