The tech advised replacements won't happen if the model you have is not in their refurbished inventory. They are not upgrading to the next flavor available or latest & greatest cause it's way out of warranty, which I get. They will replace the same model/device if they have it.
I saw a post on here after filing my support ticket that says their's SP device was not replaced b/c M$oft didn't have their model in stock, an SP4.
With that in mind, I anticipate the same response. I have an SP4 and I got mine in 2016 and I'm guilty of what the person shared too; leaving my system always on/plugged in.
The support process was easy and online. They'll ask for video of the bulge with serial number on screen. Then you upload, they review, and if they agree, they escalate amd you get update alerts.
I got 6 great, continously on, years out of my SP4. Not mad at all if they can't replace it. I would buy another but had the job buy me the SP8. Good luck to you.