Note that Opus 12 licenses work with Opus 11 (including new installs), so you can keep using Opus 11 or revert back to it if you need to for some reason, and you aren't forced to install Opus 12.
The revocation of the old licence means that you don't get an extra licence to run another copy on an additional computer every time you upgrade. The new license replaces the old one that is upgraded.
Some people assume that buying a discounted upgrade gives them an additional copy of the software (one old, one new), but it doesn't. Additional copies can be added to a license, or entirely separate licenses can be purchased, but upgrading a license just upgrades it without adding any more copies to it.
O.K., thanks. So then from the time I finalize the update order and until I install v12, I'll need to have some other file manager installed (or use the Windows one) to be able to do all the usual file management things.
May I make a simple suggestion?
Don't revoke the v11 license until the install of v12. That would serve your reasonable need of not having both v11 and v12 licensed on the same computer and yet still let the user not having to use some other less capable/less familiar file manager in the meantime.
You won't need to do anything. The old licence is revoked in the legal sense, and replaced by the new licence, but the old licence won't physically stop working. You can install the new one at your leisure.