I would urge a little caution removing the key, I had a lovely Nouveau vase that had a lump of something rusting away and fused to the base. A couple of hours after I cleaned the vase and removed the metal a huge crack developed across the base and up the sides of the vase. I heard it go ping from the next room.
I think the problem may have been the fusing of the two materials and the stresses that built up over time. Once I removed the metal there was an imbalance and the crack was probably inevitable.
Given my wee horror story, the key does not look as though it has actually fused to the glass - if there is a little movement then of course it will not be. I have removed quite a few metal objects in similar circumstances, the key got in there without it being forced and if you can gently wiggle it around, with a bit of patience you should be able to remove it. The trick is finding the spot where the opening is slightly larger - they are never entirely consistent. The key found it's way in there and the process should be reversible.
John