I don't know....If LP had to loose all their energy in the future in purpose of protecting chester's voice....I think I would prefer them stopping LP earlier then. The music direction of a band shouldn't depend of singing/screaming abilities, but of what they want to sound like. They're many rock or metal singers who continue to scream there ass out, despite the fact they're 40 or 50 years old. Screamings doesn't necessarily damage the voice. And I hate when people are making this random association : becoming older = becoming softer = becoming more mature.
Now, if LP continue making music they're enjoying, soft or not, without any boundaries like "oh, maybe should we protect Chester's voice", then I hope they'll still be there in 20 years or what. And in that case, I can see them becoming a "legend band".