Can I update my iphone that no longer has service?

I have an iPhone 4s that I bought almost a year ago with Verizon. However, a few months ago I switched back to my old phone, that doesn't have internet, because my cellular phone bill was too high. Although, I was able to use the iPhone 4s like an iPod touch. I used to it take pictures, face time, and everything else. The only thing I can't do it text and call with it, so I just leave it on airplane mode.recently, there was an update for the iPhone and I've been wanting to update it. Although, I'm worried that if I update it, it will be permanently locked and I won't be able to use it unless I connect it with Verizon again. Can anyone tell my what would happen to the iPhone if I update it?

It should be ok but i would ask someoen at the apple store they would know better.