First of all, had they produced those episodes it wouldn't have changed Crusade's fate. Crusade's fate had NOTHING to do with ratings. TNT decided they didn't want it and canned it before even ONE episode aired. That's why they advertised it as a limited series. They had decided long before they ever put Crusade on the air that it wouldn't continue past 13 episodes. Ratings had nothing to do with it.
And when it DID air, Crusade DID get good ratings. Just like it's getting good ratings now on Sci-Fi.
And it's not dead. If it were dead JMS would flat-out say "It's dead". I don't have a link, but Joseph DeMartino made a great point around here how, if Crusade were dead, JMS had ample opportunitues to tell us otherwise. He hasn't. JMS also stated once that the ratings for Crusade have nothing to do with Sci-Fi's decision to produce Rangers. The Crusade ratings only affect Crusade. So it's a possibility that the Sci-Fi Channel will ressurrect Crusade, but only based on how well it performs. (And it's currently exceeding expectations)
As for the cast, they're all available, with the possible exception of Marjean Holden, Dr. Chambers, who's on Beastmaster now. (And hey, that show may end up cancelled soon, so she may be available, too) And even if she's not available, I'm sure JMS could easily replace her. If he replaced Sinclair, the original lead for B5, then he can replace Dr. Chambers.
The cast has also been supportive of the return of the show. Most notably Carrie Dobro and Peter Woodward. Marjean Holden, Daniel Dae Kim, and the actor who plays Eilerson (His name escapes me right now) have also expressed support for the show being resurrected. The only one I haven't heard of supporting it's return is Gary Cole, and that's not saying that he doesn't support it's return. I just personally haven't heard him say anything about it.
Then there's the fact that the sets are still in storage, so no need to rebuild them.
All this tells me that Crusade is far from dead. Are the odds long? Yes. But is Crusade dead? No. And until JMS says otherwise, it still has a chance to come back.
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