If your question is if the club will go into obscurity like Leeds or Portsmouth, then no. If you are asking if we are at danger of getting knocked off the CL places and considered a top English team, then yes... someone just mentioned the example of Nokia, and that was spot on. We will gradually slide into mid-table and people will be asking "We did everything right but somehow got shafted".
Successful clubs are once that are pro-active and not reactive. The more we sit on our arses thinking Wenger will somehow turn our fortunes, the worse we are making it for us. We should have a potential candidate lined up right now for the end of the season. Give this person the entire pre-season to get tactics and formations right.
To me one thing is certain.. we are sliding into the shitter slowly every season with the clown in charge. We need to wake up!