Originally Posted by
Assam
I kinda think that idea is contradicted by Miller's statement from the time that he felt Cass had no more room to grow or develop.
Since it's a fun thought experiment, and you seem to be asking both, I'll answer both A) If I'd been put in Miller's shoes, and B) If I had to do it NOW, and skip over Cass to have the mantle go from Babs to Steph.
A) This is definitely the easier one. Assuming that Morrison had to be left unbothered and that Cass was still going to be left out of Battle for the Cowl, despite how little sense her absence made, this is what I'd go with:
Batgirl #1 has the great scene of Cass and Steph fighting together from the original, but Cass doesn't leave here. Steph goes home, while Cass goes to see Babs, and while it wouldn't make sense for their ACTUAL reunion to be only happening now, it'd be treated as a reunion for them for the reader. Both would remark how much Steph has grown. Babs would mention how she isn't the only one (referring to Cass) but getting back on topic they'd mention how she could still be even better if she only had more faith in herself. The three would do a quick mission together, and at the end, they decide to not just let this be an occasional thing anymore.
Issue 2 would see Cass and Steph going about their lives, contemplating all that they've gained and lost and the hardships they'd been put through. Meanwhile, Babs would learn of Tim's departure and starts worrying about him.
Issue 3 would begin the transition, as Cass and Babs realize what Steph needs and that there's room for another Batgirl. Steph gets her new suit and codename, and Team Batgirl is officially formed.
Issue 4 would be a fun romp with the newly named team and highlight some new toys and skills that Steph is rocking. However, we'd also see that something doesn't feel right to Cass, happy as she is for Steph. Meanwhile, Babs would have tracked down Tim, who would tell her that he's not coming home until he proves that Bruce is still alive. And because of the state he was in at the time (And the fact that he's...Tim) he wouldn't be the most polite about it.
Issues 5 and 6 would have Team Batgirl team up with the new Batman and Robin. Babs, Cass, Steph, Dick and Damian have still never all been in the same room together, and dang it, I would make the most of those dynamics here. It would mostly just be a fun two parter taking full advantage of all the rich relationships that could be built there, but towards the end, there would be the scene that sets up the final issue of the opening arc: Cass would talk to Dick about what leaving Robin behind and becoming Nightwing meant to him and the two would have a nice bonding moment, maybe even bringing up how much they both lost in Bludhaven. (Remember, I may think Dick himself is a tool, but I love how he interacts with plenty of characters.) At the end, Babs would tell everyone about how she was recently in contact with Tim and how he's unable to let go of the idea that Bruce is still alive.
This would take us to #7, which would be Cass's departure. Steph is complaining to Babs how she should let her just go kick Tim's butt and bring him home, but there's an alert. Team Batgirl is about to spring into action, but Cass says she wants to go alone. They're confused but they go along with it, Cass arriving at the site...and finding Shiva. Rather than fight for the umpteenth time (There's no point. Shiva knows she won't kill her), they'd talk, the themes of which harkening back to the Death Wish arc. Shiva would even learn that despite him being gone now, Cass was adopted by Batman. And Shiva would actually be happy for her, with even after everything Slade did to her, and despite what she was intended to be, she was still able to continue on and forge her own destiny. Those last few words specifically echoing what Dick had told her in the previous issue. Before Shiva goes (The reason she'd shown up at all WAS just to get Cass's attention having heard about the Slade fiasco) we'd get one more echo to the end of Cass's solo as Cass asks "Will you ever stop?" And to reflect how times are changing through the Batverse and everyone is growing, she'd give a simple "Perhaps."
Steph is getting antsy, wondering where Cass is, and off-panel, we'd see Cass say, "Back." Through some casual banter, one of them would refer to Cass as 'Batgirl'. To which Cass would say, "No." Cue full splash page of Cass in her new costume, revealing her new name which would NOT be Black Bat. Steph and Babs are confused, and Cass explains (Through fewer words than I'm using here), that Batgirl was the first name she ever knew. And being Batgirl is what she needed. A chance to do good to make up for what she did as a child and a chance to become part of a family. But things have changed. She knows she's a good person, while still as dedicated as ever, and she IS part of a family. Batgirl used to be who she was. Now she is Cassandra Cain-Wayne, and anything else is just codename. And the man who made all this possible for her? She can't believe he's gone either. The Bat is what she fights for, but she still loves her dad. And it turns out she's never actually believed he was gone, but unlike Tim, she had no idea where to even start looking. Cass tells Steph that the Batgirl name is now her's alone to honor, and gets Tim's current location from Babs, saying she wants to help Tim on his search, adding on that she's also worried about what being alone is doing to him, knowing full well how damaging isolation can be. The other two argue against this, but her mind is made up. She bids both Steph and Babs a tearful farewell, including a peck on the cheek for Steph, promising that when she comes back, it'll be with both Tim and Bruce. The final page would be a collage of the most important moments in Cass's life, and the most important people in it.
From there, she'd act as Tim's co-star in Red Robin, while Steph and Babs form what will be their status quo in Batgirl.
And apart from just the idea of "Cass helps form Team Batgirl", I JUST thought of all this. No the ideas aren't entirely fleshed out, but with these 7 issues, we get: A satisfying character arc for Cass which ties back thematically to her solo series, some more fun and emotional moments with Babs, Steph and Cass together reminiscent of the days from before everything went to crap, an actual reunion between Cass and Babs, Steph slowly settling into the role of Batgirl, but the conflict of her being THE Batgirl still left open, "Team Batgirl" no longer being insulting to Cass fans,the first meeting for Damian with the girls and a chance for Dick and Cass to put their recent crap behind them, and a very clear point that no, Cass isn't being kicked out as Batgirl, this IS a promotion.
Now as for how I'd handle Steph being made Batgirl today? Well that's a bit trickier, and this post already got WAY longer than I'd planned, so I'll write that out later.
Hope anyone who read though all this liked it!