If you do your job well, and the economy and the corporations you work for continue to do well, there is no reason you should not have a long and happy career as a Corporate Events Manager. The first part—doing your job well—is totally in your control. Be the best Events Manager you can be, and you won't get fired for sucking (unless you suck).
The problem lies in the second part: The economy and businesses have to do well. The reality is that when the economy suffers or when a corporation's numbers aren't where they would like them to be, things like conventions, parties, and meetings are often the first to get slashed from the budget. No events means no Events Manager.