Which religion is the first to disappear? By disappear I mean here either to disappear completely so that there are 0 followers left or that the amount of followers becomes extremely small.
no religion ever really dies. they often evolve and their popularity may wane, but they don't disappear entirely. animism and various pagan mythologies are still alive and well, though isolated. the norse, roman and greek pantheons still have scattered adherents. hinduism, buddhism and the myriad eastern religious disciplines are all doing quite well. there is no reason to believe that any of the abrahamic creeds will ever become extinct.
Really? You mean Dionysus/Bacchus are still with us? The god of parties, wine and general fun? Goody, better than the old miseries of the bible.
life is misery or didn't you notice. life is a series of trials with moments of joy interspersed throughout the general toil. every religion has known this and integrated this obvious reality into its tenets. the flip side of wine, women and song is pain, labor and tedium. the worse the everyday reality is, the better the possible rewards for persevering.