If Nemesis was never built, The theme park industry would be different, Coasters won't use the terrain as much as they do. B&M would have never developed the Dive coaster, Flying coaster and Wing coaster, And parks with a strict height limit won't have big flagship attractions.
Basically Nemesis proved coasters didn't need to be the tallest, fastest and longest etc. If it weren't for Nemesis other coasters wouldn't have been built worldwide, Think of it as the domino effect.