I don't understand the obsession over who or what will come after us, both from a scene and collecting perspective. From a scene perspective, it will eventually die and be reborn sometime in the future as something slightly different, like all youth scenes' tend to do. From a record collecting perspective the same will probably happen as well, with interest diminishing leading to lower prices for a while, then some bright spark will pick them up cheap, play them leading to demand and value rising again - A bit like what happened with trips to the US in the 80s/90s. Saying that, for sure the prices of some records in the future may never reach the heady heights of what they are now.
Those who talk about a "northern soul" legacy are either deluded or out to make as much money out of it as they can, as its just a part of general youth club-culture, that's lasted longer than others.