Hi,
You can copy instead of move. But if you need to delete a table from source base and save lookup info, edit lookup fields and turn them into static form (text, number, etc...)

So if I really want to move this table out of the base, I will lose the foreign link to this table.   

Primary/Foreign keys relation exists 'under cover' and rely on record IDs.
If you want to preserve relations with high accuracy, you can add formula RECORD_ID() in your table and reflect it in foreign tables via lookup.
By way, if you paste a list of record IDs into link field, and these IDs exist in linked table, Airtable will turn it to real links.

another option is to sync a table to the new base. After the table is synced simply delete the sync and convert to un-synced table.