Our daughter had been gone off to college and on to law school for six years before the thought even occurred to me! I guess I had always assumed that somehow she'd be back.
She was not happy about it, and definitely felt infringed upon! She had items in there that she didn't want to be bothered to go through: stuffed animals, her Breyer horse collection, clothes from high school, posters, etc! We told her, and we meant it, that anytime she wanted or needed to move back home that I would be happy to give her back "her" room but until then we were not keeping it as a shrine to her childhood since I needed space. The idea of ever moving back home seemed to horrify her and at that point she seemed more receptive. There was definitely an adjustment period for her, and feelings of loss. We continued to offer words of support, and lots of hints that we would LOVE to have her at home again...that pretty much got her over it! :-D
As for having the sewing room -- it was the best idea ever! Putting some thought into it and having DH's help in putting it together was so much fun. We painted, tore out the carpet, added electrical circuits and lighting. It became my little piece of heaven and it makes me so happy just being in there.