From everything i've seen and read, they probably wont die but thats way lower than the "sweet spot" you're looking for. I dont like to see mine below 65. If you're growing indoors the goal is to provide as close to perfect conditions as possible. If im not mistaken some strains can handle colder temps than others. One positive from cooler temps is they generaly bring out blues and purples so you should end up with some sweet looking buds!
I agree, you want to get those temps up. Ideal for lights on is 72-78F, and for lights off is from the same to 10 degrees cooler. Some equatorial sativas don't like it to get much below 67 or so.