This is just going by DP's post of the Shadow's plan, but believe he wanted it so that everyone but Severus was consumed and then as the Shadow over exterted himself Jakob would either free himself/get freed by Severus, and the two of them would beat the Shadow.
That's just my interperatation, you should probably ask DP though, since I like your idea too.
I'll talk to DP, but I think that Domon should be consumed 100% at first and the Shadow winning, but then Domon's pure natural energy "burns" the shadow away and allows Domon to hold back the other consumed people while Severus beats the (insert bad word) out of the Shadow.
Well after Anima is consumed by the Shadow, it will just be Severus and Domon, then you have to get consumed as well. So I say launch an attack at the Shadow so it accidentally messed up the plan Severus and Anima had, which gives the Shadow an opportunity to consume her.