[Angry Hill Troll]

Honestly, after total control was achieved Sauron may have decided to wipe out the unorganized scum of the orcs entirely, now having men and dwarves, and all the other races as his well-ordered pawns.

Well, Morgoth certainly would have done so, but I doubt that Sauron would have, if he had enough menial grunt work to keep the Orcs busy (I mean, you can always have them build an even more ostentatious fortress to glorify your inflated ego!).

This was sheer nihilism, and negation its one ultimate object: Morgoth would no doubt, if he had been victorious, have ultimately destroyed even his own 'creatures' such as the Orcs, when they had served his whole purpose in using them: the destruction of Elves and Men...Melkor could do nothing with Arda, which was not from his own mind and was interwoven with the work and thoughts of others: even left alone he could only have gone raging on till all was levelled again into a formless chaos. And yet even so he would have been defeated, because it would still have 'existed' independent of his own mind, and a world in potential.
Sauron had never reached this stage of nihilistic madness. He did not object to the existence of the world, so long as he could do what he liked with it...though Sauron's whole true motive [during his captivity in Númenór] was the destruction of the Númenóreans, this was a particular matter of revenge upon Ar-Pharazon, for humiliation. Sauron (unlike Morgoth) would have been content for the Númenóreans to exist, as his own subjects

Another thing: Sauron may have thought he was working for his own purposes, but it is likely that he, to was unwittingly serving his former master's aim. I believe somewhere Tolkien says that Sauron was only an agent, albeit a greater one.


On the issue of Morgoth coming back, this is rather complicated. Tolkien says at one point that Morgoth is not Melkor, rather Morgoth is what remains of Melkor's central will and power after he dispersed most of his being throughout the whole of Arda. Defeating Morgoth does not remove Melkor's will from the world, for this is dispersed throughout Arda. In fact it may not even remain dispersed, but eventually recoalesce:

We read that [Melkor] was then thrust out into the Void. That should mean that he was put outside Time and Space, outside Ëa altogther; but if that were so this would imply a direct intervention of Eru (with or without supplication of the Valar). It may however refer inaccurately to the extension or flight of his spirit from Arda.

In any case, in seeking to absorb or rather to infiltrate himself throughout 'matter', what was left of him was no longer powerful enough to reclothe itself (It would now remain fixed in the desire to do so...). At least it could not yet reclothe itself.
...
The dark spirit of Malkor's remainder might be expected, therefore, eventually and after long ages to increase again, even (as some held) to draw back into itself some of its formerly dissipated power. It would do this (even if Sauron could not) because of its relative greatness.

I agree with Keeper's analysis of the Valar's approach to dealing with Sauron somewhat indirectly, letting the Istari serve primarily an advisory role, while letting the Children carry out most of the actual struggle.