They're quite tough, but they're killable. I'm handling Mordred, since I know how he'll end, but the others are fair game. So basically make it hard and a struggle, keep them true to what I've said, but you can kill them. Go with your guts, basically.
Right, here's the basic breakdown of what happens next in the RPG, just so we're all clear:
Thor returns from consulting Odin, Galic gets back somehow, and we all set out to Avalon to fight the Mikaboshi with the knowledge Thor got from Odin.
Meanwhile, the battle continues at Avalon, and the armies of the Digital World and the Tamers get horribly massacred, and the few survivors are forced to retreat. As they pull away, the Mikaboshi proceeds to battle the Council while razing what remains of Avalon to the ground.
We arrive to find most of the Council dead, and promptly attack A-M and the Chaos Lords. Cue final battle.
That's basically all we've got left. Almost there... this massive battle of the army vs. the Chaos Lords and A-M shouldn't take too long, it's mostly to give the guy some wow, he's badass factor, so I've only really got one thing planned for it beyond the army getting horribly mauled. After that, we can get into battle and end this. Then it's just epilogue posts, tea and biscuits, and onto Devil's Ascent!