So what effect did the events of Shivering Isles have on the future of the elder scrolls world? is Jyggalag full Daedric Prince again, with plane of oblivion and everything? Is the player character going to continue being the Madgod? This is my first post so forgive me if I've asking something that's obvious.

We can only speculate, probably, probably, and it's neither obvious nor obscured so much as we run into a lack of information.
>So what effect did the events of Shivering Isles have on the future of the elder scrolls world?
Worshipers of Sheo have a different guy now, not that'd they'd care if they even noticed. Lorkhan MIGHT be free again as Sheogorath is the Lorkhan-shaped hole in the world and the gape in Lorkhan's chest (at the same time) as the hole is now plugged by a fifth-subgradient neutral entity (a mortal) rather than a fourth-subgradient Padomaic. The subgradients being AE, Anu/Padomay, Anuiel/Sithis, the et'ada, the mortals of nirn. Unless I've interpreted the creation stories incorrectly.
In short, basically none.
>is Jyggalag full Daedric Prince again, with plane of oblivion and everything?
It's implied that the prince is the plane, so I would say so.
>Is the player character going to continue being the Madgod?
That's a biiig "we haven't a clue unless a dev steps in."

The player assumes godhood as the curse on Jygglag is lifted.

But as Jygg tells him after the final showdown, this godhood is something that he has to fully grow into...You start out able to alter the weather but as you grow, the isles will more and more reflect your will.