They could just type SU in terminal emu to see if you have root lol jk but verizon probably would do that.. I would say yes if your sending in to HTC. I've heard stories where they didn't care that much anyway, I guess it depends how lucky you are but there are still signs where they can tell

 

visually,yes. for all practical purposes the phone will look 100% stock.

however,if you s-off'ed with a method that required you to htcdev unlock,then htc does have record of your imie,esn,etc as well as all your htcdev account info. no matter how completely you return to stock(including going s on ) htc technically knows that you have messed with it,and could reject any claim they feel is the result of such tampering.

for what its worth,ive not heard of htc denying any legitimate hardware claims,and have heard countless stories of folks turning handsets in to carriers unlocked,rooted,and even running custom roms.

if i had send any device for a legitimate warranty claim,steps i would take:
-restore mid and cid if altered
-remove tampered banner
-lock bootloader
-run an ruu

i would not turn s on. but if you chose to,make sure your device is able to be htcdev unlocked(i.e. not verizon) and when you run an ruu,run an old one that is s-off'able

hope that helps

 

Hi Your warranty will still be fine unless you have burnt out the cpu or some such thing connected with overclocking ETC. Even then they have to prove it was that which caused the fault. This is for all EU countries FULL ARTICLE HERE
I sent mine in with a touch screen fault dead band across the middle they said no warranty repair and sent me a photo back. Attached with the full root job showing Super cid the lot I sent the phone like that to test and i got a new phone. So i am not saying your warranty is fully covered but your whole warranty is not voided. Its a myth they want you to believe.