On one hand, this is a rather funny thing to have happen... But then again on the other hand it can lead to an argument with you and your buyer. The buyer wants a light up there, but the contract didn't even talk about it, at all...
In the purchase contract most of them require you to state what is staying with the house and what is the seller's property to being taken by them when they move...
So if you state that the chandelier is "excluded", then the seller did what the contract told them to do. The seller took down the light fixture and satisfied their end of the bargain. They have put up a light that has a bulb and a long chain to start it up.
So what can you do?
One option is to write this in the comments or additional terms section.
Chandelier to be removed by licensed contractor after contingencies have been removed by buyer and replaced with a light fixture of buyer's choice, purchase buy buyer and delivered to seller upon removal of contingencies.
Kind of a long sentence, but you (and the seller) will know exactly what to do, and there will be no hurt feelings after.
Have you ever tried this?