Can you post a picture what it looks like? I can understand if the vibrate switch just fell off on it's own like an older iPhone of mine. I just took it to Apple and they did an exchange for a refurbished. This must havve happened because you dropped it or maybe it hit something to cause the switch to go inside the phone or something? Most likely they won't replace it since this damage was caused by you it seems. Maybe they'll take off the case for you to pull the switch back. I'm sure the techs got tools there for that in store.
Hope all works out 🙂