"So what are we doing tomorrow?"
"Same thing we do every night, Pinky. Take over the world!"
What does a guild do once Illidan is down? Game's over, right? There are no more challenges, no more bosses to progress, nothing you haven't seen. You've done it all. So what happens then? What's next?
First of all, and I can guarantee you this - no wait, actually, I will bet you 100g that this will happen - right after Illidan is down, someone in your raid or someone lurking on vent will say the magic words 'so what are we doing tomorrow?'. Provided that you didn't kill him on the last day of the reset, this is. (They might try and say it anyway though, never underestimate the individuals need to say something witty-only-it's-not-really-witty-at-that-time-but-kind-of-a-bummer-to-everyone-actually.) We had two people do this, one of our Wonderbears and a Hordie lurking in our vent channel. All I can say is that it sort of breaks the magic of the moment and forces you to think about the fact that the game really is over, at least until the next patch/expansion.
Bumming as it is though, it pays to be prepared. Kamuflasjefylla had held off attuning new people to BT/Hyjal while we were progressing Mother/Council/Illidan so attunement runs through TK and SSC were naturally planned. To give the raiders a treat though, we were gonna hold off a couple weeks longer and head off to Naxxramas once Illidan was down. A few people had raided Naxx pre-TBC but none had cleared the whole thing and at any rate, they were all just as excited to see it again as the rest of us were to see it for the first time. I don't want to sound like a whiny bitch but I really do feel like more care were put into the little things in the oldschool raid instances. I don't know. Maybe I just fail to see the little things in Black Temple and Hyjal because I'm too focused on the encounters. Anyway, the atmosphere and music in Naxxramas is amazing.
We didn't do much when it came down to it - took out Patchwerk, Grobbusomething and the big doggie, then wiped a couple times on Thaddius cause one of the tanks kept getting knocked into a wall - but we thoroughly enjoyed the change of scenery. Really, just seeing some different colored walls than the brown-and-gold of BT was a relief.
For most guilds though, the immediate focus after Illidown is to cut down on raid time. As you progress raid the bosses you normally play pretty hardcore (we did 5 hours, 5 days a week) and when Illidan is the only one left you might push it even harder (6 days a week!!). The main focus we've had since we killed the Betrayer was to try and get the clearing of both BT and Hyjal down to 2 days. Not only would this give us some time off, it'd also open up for doing other things like attunement runs and farming Gruul's Lair for that elusive Dragonspine Trophy our rogues are drooling over. (I'm still hoping to squeeze a World Dragon or two into that free time somewhere!) Let me tell you this though: Clearing those two raid instances in two days is a pain. The bosses aren't much of an issue, but the trash? Is neverending. Especially the Mother ShaWaWaVoom trash - seeing all those luxurious beds with their inviting pillows is a pain when you've been raiding for 4 hours+ and you're getting really sleepy.
We've somehow managed to do it though, and these days we normally take out BT up to Council on Wednesday, then take out Council, Illidan and all of Hyjal on Thursday. Fridays I organise and raid lead a Karathon for badge-horny mains and alts in need of gearing up. Saturday is off, Sunday we sell loot in Gruul/Maggy/TK/SSC to encourage more 25 man guilds (our server still sorta sucks Alliance-side) and Mondays & Tuesdays we watch our poor raid leader bang his head against the desk as Sunwell on the PTR is down yet again. Since my Karathon project is on a volunteer basis, that means I only really raid 3 nights a week. For some, that suddenly freed up spare time is best spent out there in the real world doing... I don't know. Stuff. Things. For those of us with little to no life though, it means we get to focus on PvP or level up alts. I find myself in Outland for the second time now, as my baby warrior walked through the Dark Portal recently, and this time around I plan on not rushing it so I can actually enjoy the different zones. I also plan on focusing a lot on reputation farming, so I can get those rep rewards while they're still useful, like it was meant to be.
My point is that I think a lot of guilds fall into a trap once they've downed Illidan. Simply plodding on and doing nothing new or different will most likely wear down your raiders pretty fast, and might lead to people quitting or going on breaks. Everybody wants full t6 and even full offspec t6, but don't do it at the cost of good raiders. Give them some treats, make sure their schedule is varied and interesting. Drag them to Onyxia one day for the hell of it. Schedule a 25man Naxxramas run. Go say hi to C'Thun for old times sake. Go world dragon hunting (and take me with you, damnit!). Insert some flavor in the schedule and things won't be so bad when you step out of progression and into the unending lands of farm-raids.
And beware those luxurious beds.