I can think of several ways to do this, but all will likely require a little bit to a lot of rework on other parts of your script. So I'll throw out several suggestions and you can tell us why they don't work for you
1. Don't exit. Return an error string that the content manager displays instead of its regular content if its non-empty
2. Don't exit, redirect back to the orginal form, again passing an error message that you'l display if non-empty. also pass back (via session or get) the entered values so you don't lose them, redisplay them on the form
3. Package up the code you need for the footer / page formatting as a function and call it as needed before exiting.
I use versions of all three on my sites. Methods 1 & 2 are used for most activities. Method 3 is used when I detect "bad guy" activity and want to stop script execution immediately. (I also destroy the session, etc)
Of course on my site bad guy activity could simply be using the back button right now

as I don't have enough check to make sure resubmitting doesn't cause sql problems, so I just block certain bad page-state transitions.