How on Earth, does a human cope with a tragedy in which four family members die? [Details inside].

A few days ago an accident between two cars took place.
They crashed and both landed in a (frozen) canal, after which all passengers were taken out by the emergency workers and they were hospitalized.
Both passengers (father and daughter) of the first car died soon after.
Two passengers of the second car (two brothers) died too.
Yesterday also the mother and daughter/sister of the two boys lost their battle.
Leaving the father/husband behind (he is out of danger and out of hospital).
My question focusses on the father of the second car:
How can one ever overcome/handle such big tragedy?
I can’t begin to fathom how hurt a person would be in a case like this.
Obviously I don’t expect answers with solutions to cope with this kind of grief, more so your thoughts on how the human mind works in these terrible situations.