I was digging around for some information and found this statement from an old Las Vegas Advisor Question of the Day:

"But to finally answer your question, the oldest Strip hotel still extant is the Riviera. Actually, the Sahara predates the Riv by three years, having been built in 1952, and though some of the original casino might have been incorporated into the many expansions of the Sahara over the years (notably a 14-story tower in 1966, a 24-story tower in 1968, a 26-story tower and meeting area in 1988, and a 600-room tower in 1990), the original low-rise garden rooms were razed during a casino expansion (along with adding a new pool area, indoor racing-themed wing, and roller coaster) in the 1990s."

Sounds like a definite maybe (or maybe not) as far as any of the original casino still existing...!!