At least every awesome Hellblazer writer so far has other work happening. I'll give it a shot, and if it's just not hitting it, there's always some new Garth Ennis, Jamie Delano, or Warren Ellis I can check out instead.
(Edit to clarify: I do think Vertigo will last longer than just a year, but long-term I'm less positive.)
With Image, you completely own the property, including media rights.
With Vertigo, you give up those rights, and if the book is cancelled, you can't take the property anywhere else to be published.
It's probably more secure if you want to be published and have a steady income on the front end, but it's also the reason that guys like Ennis, Ellis, Brubaker, Fraction, etc, won't come anywhere near the imprint.
Edit: Or in short, what Darrell said.
Yep. What are the odds the new DC book doesn't last two years?
Vertigo is not going to end. Their trades are still one of the top selling books of the year and they're producing quality work, some better than anything that selling right now in DC, Marvel or Image.
Yeah this just blows.
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