Near bankruptcy? Yeah, I don't think you know what you're talking about.
Cena is the most valuable asset the WWE has, sure. But no, they wouldn't struggle without him. They'd still bring in around $400 million in revenue and it wouldn't take them long (think around 1 - 2 years) before they establish new stars.
WWE's strategy right now is bulletproof. Even with decreasing revenue, they're increasing profits. That's because of streamlining processes and improving their organisation from within.
Considering how determined Vince is in regarding Miz and Del Rio's pushes, as well as the fact that Sheamus is somewhat established, he already has people to step up sooner rather than later. All that would happen is Triple H would return and start working on establishing talent in the eyes of the fans. Within a year or two, he would succeed in elevating several of them. Add in Undertaker helping out as well as the fact that Rey and Orton are still around as big faces and WWE would cope perfectly fine.
Cena leaving is very much like Shawn/Batista leaving. WWE will take a short-term hit but they'll recover soon enough because they're the main show in town and the base audience isn't going anywhere. Don't underestimate their promotion capabilities. They made you, for one, believe Cena is far bigger than he actually is. That Shawn Michaels is far bigger than he actually is. What makes you think if they didn't put their full-force behind stars like Miz, Sheamus, CM Punk etc. that they wouldn't make you think the same thing?
They may not reach the heights of Cena but that's because they don't have as much veteran talent like Angle, Eddie, Triple H, Taker, Shawn, JBL, Edge, Batista at their peaks helping out the product. But they'll easily keep WWE stable and profitable while leading into the next generation where they'll probably create a star as big as, if not bigger than, Cena.