I don't think so. A lot of people value their IG accounts, so it's more of a trap. If deleting their Threads account means losing their IG account, they won't do it.
It's virtually impossible for this to be an accidental bug. It's just not how it works. Building the new feature so that it can't be switched back off but can be switched off is realistically impossible. It might be complicated to make a rollback script, but the lack of said code is a choice by management.
Which is why it's still not available in Europe. They're waiting until it has critical mass and don't need the dark patterns anymore before rolling it out there.