iPhone 7 Plus shutdown and restarts automatically

This is a user to user support forum and Apple does not participate here. If you saw Apple and they recommended replacing the device, they have explained your options. What you do is up to you. No one here could change that, nor answer your question about 2 year work. My wife has an iPhone 7 that was purchased on release date and it is working just fine, so I can say that Apple iPhone 7 can last longer than 2 years, however it appears there is something wrong with yours.

All electronic devices (and everything else, also) will fail at some time in their life. Most will last longer than 2 years, but it depends a lot on how well they were cared for; how many times was it dropped, for example? But random failures happen also. And a lot of users replace their phones every couple of years, anyway. I had an iPhone 4S that I used for 3 years that I passed on to my wife who used it for 3 more. It was still working when she finally got an iPhone 8, so we passed it on to a charity (I did replace the battery once). She also used my 5 year old iPad 2 until I talked her into getting a current model. The iPad 2 still works, however, 7 years later. OTOH, I had a 7+ that stopped charging after 18 months, but, as I had AppleCare+ it was replaced under warranty.

So how long with a phone last is similar to how long will a car last. I'm still driving my 16 year old Prius with 100,000 miles (or actually my wife is). It works great. On the original traction battery. I don't expect an iPhone (or any phone) to last that long, however.