FK from logged to unlogged table?

Hello,

I'm looking to improve bulk write performance on a table of about 23 million rows by setting it unlogged. If lost, the table can be re-generated from archived raw data. The unlogged table would be referenced from a different, logged, table by a sparse but very important foreign key.

If the unlogged table is lost, I can repair the foreign key data by re-uploading the raw data and following a different unique key. However, this would be annoying and I would rather not have to implement it if I can protect the keyed records instead.

1. Is it allowed to key from a logged table to an unlogged table?
2. What is the system behavior if the unlogged table is lost?
3. Is there a clean way to protect only the subset of records that are keyed? (Yes, I am considering periodic backups to an archive table, but there would still be some repair needed that way).

Thanks! Nice to meet you all.
-Dolan