I don't think we will actually be killing Yogg-Saron at all. Remember if we kill the old gods Azeroth will be destroyed. I would hate to seriously to fight Yogg-Saron this early in the game. It is an old god. It should be powerful just like C'thun was.... Well C'thun was impossible to beat until they nerfed him but that is what was so great! Though, I think if we do fight him it will be like C'thun and just part of him.

/sigh

If we kill every single old god, we have a problem. Yogg-Saron has affected (effected?) too much of Azeroth to be aloud to live. Also, the lich King hates him so....

i'm not a grammar nazi bu ti find it intrestin gyou had the effect, affect debate and then miss... aloud(allowed)

I'd like to think that one of several things will occur.

1. The final boss is Yogg-Saron and we will need to kill all the guardians to get to him.

2. The final boss is Yogg-Saron but we need to kill/subdue a reconstituted Loken or mind controlled Thorim to get to him, to do this we'll need the help of the other guardians to whom we'll have to fight to release before hand.

3. By a similar token to defeat Loken we'll need Thorrim and to release Thorrim we'll need Hodir, Freya, Tyr and Mimir whom will either sacrifice themselves or be too tired to help us fight ol' Yoggy-wogs!

I should imagine Freya will be an interesting fight, likely she'll heal herself via some mechanic, possibly via those walking plants that will most likely be adds, if not smaller sapling versions.

Hodir I have no idea, i should imagine he'll be our first fight. A simplish tank and spank or a slightly more complicated Archavon or so maybe?

Tyr? If my memory serves in Norse mythology was said to have only one arm, sometimes his missing arm was replaced with a blade or sword that stemmed from the elbow. If i recall correctly this was because in any battle only one side could be victorious and it was he who would decide the outcome of most battles.(If other gods didn't intervene) I imagine his fight will be a complex and messy affair possibly involving multiple tanks who have to swap aggro?

Mimir though i'd expect to be as the article describes, an almost comical mechagnome zergfest.

This is assuming it's not even more complicated than that, possibly we'll get in there to find Tyr, Freya and Mimir are dead already and Hodir is simply held captive in some prison while Thorrim is being beaten senseless. Maybe Freya has been set to work and enslaved into raising nasty life forms while the others serve as mere body guards. Possibly we'll have multiple bosses we've never considered and we end up fighting Freya, Tyr, Hodir and Mimir in a single boss fight, just before Thorrim who'd be just before Yoggles.

Even then we could be completely off base, maybe we won't fight Yoggers down there at all. Maybe we'll just meet him briefly and discover he's in a completely different raid, under the failed world tree? under Icecrown? Who knows.
Blizzard have a lot of ways to go with this really.

Whoops!
Wherever i said "Guardians" i meant to write "Watchers" my mistake.