Not all were unlucky enough to be killed during WWI, and ironically and almost for sure a twist of fate, one man was to survive more than one episode in his life.
Charles Herbert Lightoller was third mate and survived the sinking of the Titanic in April 1912, in fact being member of a lifeboat crew he was able to facilitate the rescue of passengers and of course save his own life. Cooperating fully with a disaster inquiry, he was able to return to sea. A reservist at the start of the First World War, he was called into the Royal Navy and was decorated whilst under the command of and in command of various ships. He was promoted and retired in 1919, although continued to excel himself, being a member of the civilian rescue party at Dunkirk.
Dying over forty years after the sinking of the Titanic, now that was luck !
World War One 
All true. I’ve also seen a note that just before WWII kicked-off, Lightoller secretly surveyed the coast of Europe for the Admiralty, in his boat Sundowner.