I know two people who lost a lot of weight and look just like you described: sunken, hollow-faced, and not necessarily 'healthier'. It worried me. They might be healthier based on lab results, but they don't look it. Weight loss is a big stress on the body, and skin might not bounce back...
I dropped 115lbs. What helped me was lifting weights and eating enough protein. I didn't want to look like a deflated balloon. I'm now almost the weight I was in high school and stronger than ever. Also, my face went back to normal after a bit.