You will need to get the install codes from AC.
Having to wipe the drive is EXACTLY the reason why several of us recommend virtualizing your AC server install, as you can go right back to the clone/snapshot you take before you attempt the upgrade.
I will tell you that a 9.1 install is statistically more problematic than 9.4.3.
Once you get AC operating again, I encourage you to backup/image the ENTIRE server so you can rollback if you run into problems in the future.
