BDD is an illness where much of the pain comes from other people. In an apocalpytic one person in a deserted world scenario bdd would be mostly irrelevant. Part of recovery then is to unhook one's sense of self worth and self value from other peoples' perceptions of you.
Even if one comes to believe that they are in fact attractive one puts oneself in a situation where a dirty look or even a spiteful remark can wreak havoc. The only way forward is to reach a state where you essentially dont really care how others perceive you.
CBT would probably be the most effective means of approaching this. Avoiding social media, comparisons, avoiding tv as much as possible, diverting thoughts away from self-obsession.
The treatment would be similar to that which is used for OCD given that BDD is one manifestation of OCD.