I know all the people dieing isn't a good thing but from reading the argonian account i got the impression that Black Marsh is off a lot better without outside influence and just lives on it's own.
Though seeing as ore extremist groups started to form this might also be a bad development.
EDIT: I just thought of one thing, after the destruction of Vvradenfell wouldn't the (already high) prices for Dwemer, Glass and Ebondy equipment skyrocket now? While Ebony and Glass can come form other sources and there are Dwemer artifacts outside of Morrowind (even thoug much rarer) Vvradenfell was as i recall it the main source for these materials.
Now that Vvradenfell is in ruins and the mines for it are probably either destroyed or inacessible delieveries must have drastically reduced.
From the sound of things, Black Marsh was already more or less free of Imperial influence before Umbriel arrived. The Al Xileel (spelling - don't have the book on hand for reference) organized the Argonians during the Oblivion crisis, booted out the Imperials, and then fell upon the already beaten carcass of Morrowind. Extremist or no, its nice to see a party in power in Black Marsh that is by the Argonians, for the Argonians. Assuming Umbriel didn't destroy too much of Black Marsh, its starting to look like the Argonians are on the rise in Tamriel.