Stephen King speculated about this a little in his time-travel novel “11/22/63”. From what I recall the USA went into a dramatic decline and became a 3rd world nation, although this wasn’t really the focus of the book.
Unfortunately I believe that if Kennedy had survived the first assassination attempt there would have been another one before long. The people who were trying to kill him would have succeeded eventually. Needless to say I don’t believe that JFK was killed by one lone crazy guy with a mail-order rifle, anymore than I believe that Jack Ruby killed Oswald in a fit of patriotic rage.
I enjoyed most of the book. However, it falls apart at the end. King's description of what happened in the years between Dallas and the present time is not very realistic or believable. I wound up only giving it three stars when I rated it for Goodreads.com.
Any facts to back up Oswald was not acting alone?