Why Talibani and what's he probably gonna do?
Because this issue is up to the President of Iraq (who usually has a largely representative role). He won't oppose the death sentence, since he already has indicated that, despite his opposiiton to the death penalty, Saddam deserves to be executed a thousand times.
The death warrant has to be signed by the President, and that's Talibani. Maliki is only Prime Minister.
Talabani personally opposes the death penalty in general, but he's allowed the vice-presidents to sign on his behalf for other recent executions.
I imagine great pressure will be put on him by the Ramsey Clark types in a last-ditch effort, but I'd guess he'll personally sign this one. He's a Kurd.