I don't think many ordinary people would have the slightest idea how to stop the bleeding from a severed leg.
In the same way as other bleeding and that's first aid basics (if they don't know then they should at least read about it - even kids are taught first aid at school):
Cargo said the poor guy's intestines were out of his body
Right, sorry, I forgot about that :/ But stopping the bleeding from the stump wouldn't hurt. People can survive some pretty shocking injuries, so you never know... It's better to try and do sth than not do anything, imho...
you could say the Act of Contrition on their behalf
I doubt I'd be able to do that, holding his hand would be a feat already...
were in obvious shock, some vomiting.
Those men taking pics clearly weren't vomiting and were composed enough to take pics of a dying man... It's just... I have no words for that...
Btw, if the witness of the accident doesn't know what to do, the dispatcher should be able to inform this person by phone what to do, how to help the victim until the ambulance or the police arrives.
And here's a first aid video in case of leg's amputation in Polish (with presentation):