Headling and the roof are not one piece, so yes you should be able to stick the headlining back up and you wont need a new roof just because the headlining is loose.
If that's a real CC model (he described it as coco chanel, but it's really called a Christmas Convertible

) then he's completely ruined a pretty rare mk1 cabby.

The original roof will of had cc decals on it but that's probably long gone as they only made these for one year and the roof is impossible to get.
Don't forget it's got no mot or tax so I'm not sure it's even worth £450 if you want me to be honest.