Hello Rabbit there are a few wierd things.
1st how can you damage only the rearwheel and miss the object with your frontwheel ?.
2th don't you worry where the nipple of the missing spoke has gone?
You say it is drivable does that mean you feel something riding the bike that is worrying?
If there is any doubt about the rim and/or spokes I should replace them all, you cannot pull out a flat spot
with a new spoke,and how are the other spokes?.
It is your own safety that you are dealing with.
good luck with it.
regards George the second