You are replaceable. It's a fact. It holds true for everyone. You can and will be replaced. You're not so special and unique that we can't find someone else to fill your place. There' s always someone smarter than you. There's always someone better than you. The best you can hope for is that your replacement doesn't come along before you are ready to leave, or that your superior doesn't realize that you can be replaced for a younger, smarter, cheaper model.
However, when you are replaced you then get to be someone else's replacement. Fortunately, there's always someone older, dumber and more expensive than you. So don't worry too much, because you'll find a place. If you don't, then there is a very good chance that you are the dumbest or the worst in your field.
If you don't believe me, just look around. What if you didn't show up for work for two weeks? What would happen? The economy certainly wouldn't fall apart. The world wouldn't stop spinning. Everyone would keep on living (or dying) and no one would be any the wiser. Sure, your boss might be a little annoyed, and your company would probably fire you but there would be no major catastrophe. In fact, your company would just hire someone else to do what you were doing and everything would chug right along like it had before. Except that you're probably a little more tan from your unannounced two week vacation.
This idea is the whole reason we have unions. The workers realized that there's always someone ready and willing to step in and replace them - often for less pay - so they got organized to keep this from happening. They're still replaceable but it's a lot harder to replace them.
You say, "But I'm me and there's no one else like me, so I can't be replaced entirely." Sure you can. It happens all the time. People die. What happens? They get replaced. Sure, people are sad for a while but they eventually get over it and move on. You wife will find a new husband. Your friends will find a new friend. Your co-workers will find a new co-worker. Or they won't - which is the saddest of all. Maybe they won't even try to replace you. You may think that is an indication that you are not replaceable, but I say it's just and indication that you were never needed in the first place.
Sorry, folks, you're just not that important.