Have you ever used a 'registry cleaner'? (a misnomer if ever there was one). If you did it may have created a registry backup which you can use to restore the registry to a time prior to making changes which caused the the context menu to go pear-shaped (yes, same as US idiom "go south").
Even if you didn't you could try running Windows System Restore which can be used to wind back the clock as well. The only difference between the two is that any programs which were installed after vlc disappeared from the context menu will have to be reinstalled since the restore operation will delete them.
Over the years, have used several, but of late only use the one bundled w/ Ccleaner. Moot point, though, as i rarely backup before the clean. This HAS caused me to think though, perhaps if I uninstalled VLC, and then manually removed every reference to it from the registry, I could successfully reinstall it, and all would then be right w/ the context menu again. Although, as i type, that solution probably would not suffice, as the program itself technically never uninstalled the last time I did so (scroll back, if you are new to this thread), which was utterly weird...
Are there any threads on here about uninstalling VLC, I wonder?
No luck w/ System Restore. Maybe I should start using that again.