"... the page disappeared..."?

If this is about getting a bonus for using the Search function, the page doesn't disappear; it sits there until you move off it. A couple times, I have moved off a page before realizing there was a Search bonus. I hit the Back button on my browser & input the code, no problem.
Of course, if you don't respond in a timely manner, the bonus expires. (I think it's around 3 minutes, but I'm not certain.)
Also, if you input a non-matching code, you'll get a new code, but only 2x (3 chances in total).

Are you maybe talking about a SwagCode? That's a bonus that appears on an otherwise normal page. And again the page doesn't disappear. If you take too long, you get an expired notice in the SwagCode box, but the page remains.