I've removed and replaced keys quite a bit on chiclet keyboards, so I could tell you at a glance whether the keys can be put back on. The most likely problem is that the tiny plastic hook at the end of a hinge leg has snapped off. In the past I have sacrificed a different key of the same form factor to replace the hinge -- this might be an option for you. You might also post the make/model of the computer and see if anyone has a junker you could salvage key hinges off of.