Sebastian Shaw might easily survive [Spoilers!]
Spoilers:
Putting a piece of metal through someone's skull and brain at low speed wouldn't necessarily kill them. Bullets through the head kill because they carry a great deal of force - they shatter bone and send fragments through the brain with great speed, they travel through brain tissue so fast that their passage creates shock waves that disrupt neurons and blood vessels. But a small particle traveling at low speed would break the membranes that encapsulate the brain and cause the leakage of cereberospinal fluid, and would break any neurons or blood vessels they travel through, but even that might not be fatal if it missed the major blood vessels and someone stopped the leakage of fluid and gave antibiotics to treat the infection that would result from a foreign object in the brain. But Magneto's coin seemed to go down the center of the brain, if it passed right through the longitudinal fissure it might not do much damage at all.
They could easily bring Shaw back.
“Seventy-seven courses and a regicide, never a wedding like it!