Losing My Iphone!?

I possess an iPhone 4S. I am happy with it, it works fine and I see no need to help Apple's profits by purchasing a newer model. However, I have one definite problem and one potential problem for which I would like some advice and help.

My first problem is that I am still using iOS 6.1.3. I have never updated from this because of the known fault with the iPhone 4S. New updates would check the iPhone is working properly. It will detect the iPhone's hardware issue with WiFi and stop my iPhone working. Not only do I know this but have been through this issue with my partner's iPhone 4S. The problem this causes me is some apps have stopped working because of my iOS version such as Whatsapp and other apps I cannot download from the Apple Store because they only work with newer versions of iOS. Is there any fix for this? What options do I have if I updated my iOS and it stopped my iPhone from working? (The solution with my partner's was the iPhone was directly purchased from Apple and the fault occurred not long after the warranty expired. After a long argument with Apple they replaced the phone. My phone is much older and was not purchased from Apple but from a mobile phone retailer.)

The potential problem I may have is as follows. I have been told by my sister that soon Apple are going to stop older phones, e.g. iPhone 4S, from working. Is this true? I have good reasons for believing it is probably not entirely true but there may be some truth in there somewhere. Am I looking at owning a non-functioning iPhone 4S in the near future?

 

You could uninstall those apps and install older versions.
That's if you aren't concerned with potential security risks.

 

Sadly, that often does not apply. They will simply stop working once support for older iOS versions end. Whatsapp for example have made that crystal clear.