Will this phone keep working even with a inactive S/N?

I bought this 13 Pro to tide me over until September. However, my FaceID was weird and I called Apple to have them take a look at it to see, and we found the S/N was bad; that was the final straw for me. I called eBay, and the seller denied my refund ACCUSING ME OF REPLACING IT when I never did despite having concrete evidence it was not me, and now I am appealing with eBay. I need to see who I did it with (Apple Pay or PayPal) and plan the dispute there if all else fails and then go to the top if need be but if I lose on all 3 fronts and decide to cry in a corner about this and keep the phone will I run into activation issues later on on the Apple servers?

I know Apple will not repair it, but that's fine as we know how to clone things like battery IDs and TrueTone data... Until FaceID dies, then the phone is permanently crippled.