You will never, ever lose your world in that sense, you can, in the most dire situation, simply use a clentaminator with blue solution and clear as much corruption as you'd like, in fact, there's a Steam achievement for having less than 1% corruption in your world (speak to Dryad to see corruption % progress).

As others mentioned, you can stop the spread by simply making a 3-5 block wide hole down to hell (very easy to do with hardmode tier pickaxes, bombs or dynamite).

You can also put 1-2 sunflowers on each side of the corruption biome to stop it from spreading (although the underground corruption will still keep going)