Read the other day that Die Hard was originally pitched to Arnold Schwarzenegger as Commando 2. The screenplay by by De Souza and Frank Darabont was based on the Roderick Thorp novel 'Nothing Lasts Forever' which featured detective Joe Leland visiting his daughter at her place of work the Klaxon Oil Corporation in Los Angeles, while there terrorists take over the building and Joe fights off the terrorists one by one with the aid of Sgt Powell ans LAPD officer who is outside the tower block. Schwarzenegger who had just done Conan the Destroyer wanted to avoid yet another sequel as he had not got favourable reviews from his Conan sequel.
In the final movie Joe Leland became John McClane (Bruce Willis) and his daughters character was changed over into his wife.
Other than that the story of the novel is pretty much what was filmed I have read, including a lot of the dialogue.'Nothing Lasts Forever' was the 2nd outing for Joe Leland having appeared in Thorp's other book 'The detective' which was made into the 1968 film of the same name featuring Frank Sinatra as the title character.
Interestingly the year before, Schwarzenegger had worked with Die Hard director John McTiernan on Predator, so he could have quite easily ended up being John McClane if things had been different, I wonder if I'd have liked Die Hard as much with Arnie ? Probably not !!