Q: Sri is gone on iphone 4S what can I do?

Check Settings > General > Siri > Siri: ON?

and Settings > General > Restrictions: OFF > Siri: ON?

Did you also check in Restrictions?

Are you sure you have iPhone 4S?

Use the iPhone serial number in Settings > General > About > Serial Number

here to find out

https://selfsolve.apple.com/agreementWarrantyDynamic.do

So there's no Siri in Settings > General > Siri? and no Siri in Settings > General > Restrictions> Siri?

And you also checked that is indeed a iPhone 4S here with the serial number https://selfsolve.apple.com/agreementWarrantyDynamic.do

Note: Siri is not an app (it's built-in) and there's no Siri icon. You activate it by pressing the Home button a bit longer.

Well then figure it out yourself.