Yes! You can purchase the sale without having a fully repaired Museum. You will receive all of the items you purchased! Artifacts and Artifact Crates will be sent to your inventory so you can claim them when the Museum is repaired. Any Museum Resources like Supplies, Researchers, Benefactors, Blueprints, or Mysterious Fragments will be sent to your Museum building. They will be ready and waiting for you to use when your Museum is repaired.