Q: siri gone after update to my 4s

Make sure Siri is on...

Settings > General > Siri > Siri On.

http://support.apple.com/kb/HT4992

If no joy...  Try This...

Close All Open Apps...  Perform a Reset... Try again...

Reset  ( No Data will be Lost )

Press and hold the Sleep/Wake button and the Home button at the same time for at least ten seconds, until the Apple logo appears. Release the Buttons.

http://support.apple.com/kb/ht1430