Al Qaeda. Remember them? Well, they’ve not recovered from the death of Osama Bin Laden – but they haven’t gone away. In this week's episode, Tim Marshall explains why terror groups such as Al Qaeda and ISIS still survive even when their leaders are killed. Abu Bakr Al Baghdadi's death further weakens ISIS - but it doesn't mean the terror group will collapse. Al Baghdadi and Bin Laden are examples of ideology surviving leaders.