From the title, what was the original plan to go back to earth after dropping the payload? From my perspective, the payload is attached to the shield, if my perspective is correct, isn't this a suicide/sacrifice mission to begin with?
The payload is the large shield at the front, but the Icarus II also sports a secondary shield that protects the crew on their return voyage to Earth.
The plan appears to be fly straight toward the sun, release the payload, then perform a powered acceleration away from the Sun and back towards the Earth.
And yes, I'm aware that that makes no sense unless your Δv is huge