What kind of "upgrade" could be taking 48 hours and counting? Don't they have rollback capability to go back to previous working version?

The only thing I can think of would be some big database migration that went awry and they don't have strategy to roll back.

But normally you would get a dump of production database and test your migration scripts on test/staging servers against latest snapshot of prod data.

You don't just run migration script on your production database and see what happens. You try running it against last backup / snapshot of prod data first.

What else could it be?