The winglets are definitely removeable. I found
this picture of a KL 744F operating without winglet (and the caption suggests on one side only). And then a rather
spectacular picture of her flying with winglets.
I was looking for a picture of an LH pax -400 which I know was photographed operating without at least one winglet, but couldn't find it.
If -OEE is still out of service after a week, I have a suspicion that there is something more serious afoot than a damaged winglet.