I feel you.
Well the easiest way to prove it for *yourself* is when you call for your claim (if you haven't already) they ask 2 dozen questions. None of which is did you root/mod phone. Was that way last time for me anyway.
Interesting, I haven't made a claim yet. Will I have to return my phone if it is water damaged? If so, won't they notice that its rooted?
Yeah you'll have to return it.
Those phones go straight to 3rd party refurbisher's mega-complex to be stripped of all noticeably used parts & reset. They don't turn them on until after they've done most of the work so even if they cared (which they don't) it would be too late.
I promise you you're good as you sit right now but I gotta get out of here before I get banned for posting. Good luck & hurry up & make your claim so you aren't without a phone for multiple days!