Irrelevant to the thread, but Gallowglass, I just had to ask, I love your icon, is it a Dark Elf or a Mazkan, though. Was not sure. Uber cool either way.
Dunmer
Back on topic, this is what I think Tamriel will be like on the collapse of the empire:
Morrowind has another Tribunal - House Hlaalu, House Telvanni, and House Dres. The former will have lost much of its army in fighting the civil war, and the latter will be bankrupt as it relies on slave labour. House Telvanni will lean far more to traditionalism now that they cannot stay out of politics, and will apply their rules to much of Morrowind, restricting the movement of Imperial goods and trade but allowing Dunmeri traders to earn a fortune. The Kingdom of Morrowind will possibly be renamed the Kingdom/Khanate of Resdayn, and will continue raiding Black Marsh for slaves.
The Renrijra Krin and their support amongst the tribal chiefs has brought northern Elsweyr under the control of the insurgents, who now have ambitions other than reclaiming the land around the Niben, and Leyawiin and Bravil have lost any political support they had (and they didn't have much) as they are far from the disputes of the other cities of Cyrodiil. Southern Elsweyr will probably be at war with Valenwood, and will be ruled by an Imperialised merchant class who act as advisors to the Mane.
Summerset Isle will be ruled by local warlords who are allied to the kings of the major cities, and Skyrim will be in a similar position. Orsinium will be trying to prove itself as a legitimate city, and will either strike out against the Redguards and Bretons in an attempt to consolidate its position as a sovereign state or attempt to make an alliance with either them or a Nordic city.
High Rock will be in a similar position to Summerset Isle, perhaps with less local warlords, and I doubt that places like Black Marsh will have changed much.