I'm trying to imagine why you care whether the user views all the output...

But anyhow, what if the user enters Q or Ctrl-C or Ctrl-Z or ! pkill more?

Update:

   $ man more
   EXIT STATUS
     The following exit values are returned:

     0     Successful completion.

     >0    An error occurred.
    --More--(90%)
[download]

And (at least) the following are considered successful completion:

• q, Q, or <backspace>
• paging through everything
• when there is no need for paging, like more /dev/null