Secondary Account migration then deletion

I have complete the migration of my secondary account - to finally move all purchases to my primary account.

Lots of logging in and out on lots of devices but all good - it worked, didn't break family sharing etc - great.

I am now a month past that and was thinking - great - I can clean up and delete the old secondary account.

When I go to deactivate or delete the old account is ays that it will undo the migration!

Am I understanding correctly that I will forever need to keep the old account alive, just never logged in anywhere?