Phone updating overnight and woke up to complete dead phone.

Hi,

I have an iPhone 7 Plus that needed a software update and it was notifying me that it would be done overnight so I left my phone on plugged in. When I woke up, the phone was completely turned off, all the resets do not work including the holding the power button and the volume down button. I went to apple store and they said I needed to replace the whole phone. I feel like there could be something else that could be done. Is it completely gone? No way it just turned off and went dead. I’ve tried plugging into my computer via itunes and still no reaction from the phone. I need some guidance. Thanks!