One interesting example of traditions being revived might be the Historical European Martial Arts community: there is no unbroken lineage of teachers who would have kept the art of fighting with, say, 15th century weapons alive to this day. However, there are surviving manuals that were written by masters of that time, and communities have sprung up which have taken the manuals, started training according to them, and turned the whole thing back into an actual living martial art where people are once again figuring out the best ways to fight using these weapons.
One interesting example of traditions being revived might be the Historical European Martial Arts community: there is no unbroken lineage of teachers who would have kept the art of fighting with, say, 15th century weapons alive to this day. However, there are surviving manuals that were written by masters of that time, and communities have sprung up which have taken the manuals, started training according to them, and turned the whole thing back into an actual living martial art where people are once again figuring out the best ways to fight using these weapons.