- Could Radagast have made a big difference? I guess he could've slowed Sauron down but I doubt he would've lasted long.
I doubt, he'd have achieved anything. Radagast failed at his mission in his own way (basically stopped caring about the fate of Middle Earth and turned to animals or the wild), thus since even Gandalf the White is inferior to Sauron with the One, what match is Radagast to the power of Mordor?
- What would Sauron have done with the fortresses he took (Minas Tirith, Dol Amroth, Erebor, Helm's Deep, Rivendell, Mithlond)?
I'm not sure if this applies to everyone of those places, but why not expand your base of operation?
In general, Sauron turned out to be pretty practical, and these fortresses often control their general vicinity: Minas Tirith basically controls the mid-point of the Anduin (considering he has access to Minas Morgul, Osgiliath and Cair Andros), Dol Amroth controls the fiefdoms of Gondor as well as giving him total control over the lower-part of the Anduin (again considering he has Umbar) AS WELL as grating him another entry point into Gondor (besides Cair Andros & Osgiliath).
Erebor is like the only fortress in the north of Middle Earth as well as the best place for a slave fortress for all the Dwarves and Elves of the north. I guess, the ressources are pretty rich, since the Dwarves chose to build their main kingdom over there. This also basically answers the fate of the dwarves and elves of the north (at least of Mirkwood).
Helm's Deep he might actually demolish, since it rivals Isengard's position and Isengard is the best fortress to rule over Rohan and Dunland, also giving access to Eriador. On the other hand, the Hornburg is incredibly usefull for him, since he has direct control over the mountains and the people of Rohan living there. (Remember the battles at the fords of Isen, it was mainly Isengard's strategic location that granted Saruman victory there.)
Rivendell and Mithlond he'd probably destroy. Sauron can rule northern Eriador from Fornost, Carn Dûm, the Etten-??? (what's their name in english?). Also, both are very holy places, he has no use for, also considering, Eriador is pretty empty and I'm not even sure if at least Mithlond is a real fortress. Actually, Isengard might even be enough, but since evil spirits still exist in the north, why not reestablish Angmar? He then basically sandwiches Eriador between Dunland under Isengard's control and Angmar. Possibly add Fornost and Weathertop and the north is secured, once their resistance is crushed. (Which shouldn't be strong to begin with: Saruman's men are still occupying half of the Shire and the Dunedain are all wiped out, since Sauron won at the Black Gate.)
Actually, I'd like to talk about the Lord of the Nine. Would Sauron be able to resurrect him? I mean, his body is destroyed, and he is still originally a human. It's not a fallen Ainu like Sauron who can form another dark body when he has access to the One.
However, it's still the master ring, so he might still be able to revive him OR (which I find more probable) create a new one what he should definitely be able to do, since he has the Master Ring. Actually, and I know this is just speculation, but why not give the ring to some of his most glorious human servants like the Mouth of Sauron?
Since they are all crazy for power anyways, that could very well happen. And I believe there could be some candidates, remember, the character of e.g. Gothmog is very unknown in the books, I doubt he'd turn out to be an orc. (Probably either a Nazgûl or another evil man. What do the linguists know about the origins of this name?)
I mean, don't get me wrong: Sauron not having access to his most deadliest servant is immaterial to his victory! It should only slow him down, although considering I absolutely ADORE the concept of the Nazgûl (in my opinion Tolkiens only great villains!), I'd be eager to see the Witchking in action while Sauron has got the One!
Now, the funny thing is, as much as I'd like to write something, I can't think of anything... The point is, Sauron with the Ring (considering all the power he has already collected in the WotR) is so much stronger than any opposing force, it's basically Mordor steamrolling over everything!
There might be some brave resistance, but after that Mordor's shadow would wipe this memory and embrace Middle Earth in darkness and desperation, Sauron's central theme. I mean, it's hard to remember, how brave your king or whatever fought if he a) is dead, b) desecrated and c) you're living in slavery, so don't stand there reasoning and get back to work you lazy maggot!
Some elves might end up lucky and make it to the Grey Havens, but after they are gone, it's Sauron for breakfast, lunch and dinner and nobody will be able to break his reign. So in a way, there is nothing to say really: It's gonna be first a slaughter and than just cold, dark nothingness untill either Middle Earth is a spoiled wasteland or Sauron reaches the industrial age and starts launching nuclear rockets at Valinor^^
You know what, the last sentance was obviously a joke, but coming to think about it, it bears in interesting development: Following the books, Mordor is the most modern faction in the WotR, having access to gunpowder / mines (since they blow up parts of the Rammas in the siege of MT), and having developt sort of an industry in Gorgoroth. This theme is mostly known for Isengard, because that's their movie element and for the sake of uniqueness, it can't be Mordor's theme to. Yet, in the books, Saruman's only achievement is him creating a mix between orcs and humans and giving it a fancy name, while most of his inventions are actually copied from Mordor / Sauron.
What makes this interesting to me, is obviously the question: How much would Sauron f*** up the mystic realm of Middle Earth using the spoiled part of fairly modern technology after achieving total victory? I mean, he has all tools to his disposal, and while not really needing them anymore, his greed and malice might make him use these devices just to collect more power for powers sake.
Seriously, considering the basic theme of Tolkien's good guys is restoring lost glory, the themes of evil differ quite a lot between Morgoth whose theme is corruption and spoiling of good works (Melkor has still a creative element for some parts) while Sauron's theme also reaches into the theme of advances in weaponry and surpassing his master. His works on trolls (Olog-Hai) as well as on the big uruks of Mordor show a lot of refinement -yet not in the creative sense of good (crafting beautiful objects mostly without an actual reason), but rather in the spirit of perfecting weapons and causing more death & destruction. On that note, Middle Earth might end up as a wasteland for all of Sauron's twisted inventions.
Henceforth, as you can see, Melkor (dear attendee of this forum), there is something we agree on. This is something that ought to be celebrated
Run! Everybody run! The end of the world is approaching!
Greetings
Melkor Bauglir