What does Pip's benefactor risk by coming to England?

In Chapter XXXIX, Magwitch tells Pip that he faces the death penalty if he is caught in England after having been transported to Australia for life. 

“I was sent for life. It's death to come back. There's been overmuch coming back of late years, and I should of a certainty be hanged if took.”

Then in Chapter XL, Magwitch again affirms that he faces death by hanging if he is caught in England.

“And so I swear it is Death,” said he, putting his pipe back in his mouth, “and Death by the rope, in the open street not fur from this, and it's serious that you should fully understand it to be so."

Although Pip tries to escape with Magwitch to the Continent, Magwitch is ultimately captured on the river by police who have been alerted by Magwitch's arch-enemy Compeyson. Magwitch is badly injured when he leaps aboard the pursuing galley and drags Compeyson into the river, where Compeyson drowns.

Magwitch is ultimately sentenced to death in Chapter LVI in spite of Pip's and Jaggers' efforts to save him, thus proving that Magwitch was correct in believing that he was risking his life in coming back to England to see the gentleman he had made with all his hard work in Australia. Magwitch escapes death by hanging when he succumbs to his injuries and dies peacefully in bed with Pip by his side. 

The scene in which Magwitch is sentenced to death provides a grim picture of what British justice was like in Dickens' time. There are thirty-two prisoners, including a number of women, who are all given the death sentence in one session.