If you like living on the wild-side you can try forming it back into its original position. The headliner needs to be removed and moistened in the affected areas. You can then dry it out, up-side down, with weights in the center to push it into the right shape - you need to account for some spring-back too.
If you're asking this question though, you'd probably be better off replacing it or having someone do this for you. It's a bear to remove on a W460 and I can't imagine a W463 being any easier. I tried epoxy resin & fiberglass on mine - it worked only marginally. I should have at least started with the moisture technique.
"The way you think is the way you live"