From personal experience as a DBA: the effort usually consists of not deleting rows out of the database. The expense is a few cents a month for gigabytes of data.
Worst case scenario, the companies will simply set up a separate data warehouse style data store, and make it available to anyone who wants it internally. If we as consumers are lucky, they will scrub the data of PII before moving it to the data warehouse.
They will probably put it in some archive where they delete it after 10 years. Or they keep it somewhere on a drive where it could be accessed but will never be, since no one has a reason to use the data.
Worst case scenario, the companies will simply set up a separate data warehouse style data store, and make it available to anyone who wants it internally. If we as consumers are lucky, they will scrub the data of PII before moving it to the data warehouse.