I’d say they’re at risk, because the OS and hardware will evolve out from under them.
You can run Visual Basic 6.0 on Windows XP, but even that’s close to the end of its life (it keeps being revived on its death bed).
Those Cobol applications still live because the mainframes they run on aren’t going anywhere. “Big iron” was built during a time when computers were expensive and rare and had to run for 20-30 years. Not true with applications based on PCs and Windows, which are viewed as more disposable.