Scotch does not go bad even when opened.
Scotch does not age like wine does so you can keep an opened bottle of whisky for 100 years and it will still be safe to drink.
But most people will drink the bottle of whisky whether opened or closed well before the 100 years so it should not been an issue.
As long as you keep the Scotch out of direct sunlight the Scotch Whisky will not deteriorate even for 100 years or more.
Wine does go bad once opened and if you open a bottle of wine it should be used up within 2 years before it goes bad.
Also once you open a bottle of whisky it will keep at it's best for 2 years as long as you keep it out of direct sunlight.
After 2 years of being opened the bottle of whisky can lose it's taste and it may not be as good to drink.