The wounding system (years ago) used to work that a seriously wounded hero was a dead hero. But some years back, we changed how the wounding system operates behind-the-scenes. This means heroes don't die when seriously wounded, but need to get *more* wounded than seriously wounded, to die.
That's, IIRC, not exactly true. For hero death in battle, I believe getting to the seriously-wounded threshold is still enough.
For all other wounds, heroes are treated exactly the same as everyone else.
And no, infiltrators will never be able to kill a character that's not otherwise completely mortal.