I think it depends on the reason you're retiring the video. Is the content outdated and no longer relevant? (most people won't care, in that case). Are you embarrassed by its quality? Do you have a better course to offer? (give them that course instead).
I think offering a download window is a good solution, but if you're embarrassed by the content and don't want it out there that might not be the right solution for you. You can also offer a credit for the course -- "this course is no longer available but we're giving you what you paid for it back in a credit to use toward another course" kind of thing.
The best least-cost strategy, regardless of what particular solution you choose, is to have the customer opt-in to the solution. If your solution is reasonable, most will accept it. If the content isn't relevant, most won't care. And the few that do care and voice upset, you can deal with on a case-by-case basis without having to give away the whole store to everybody.