If it is possible, under Alabama election law, for Luther Strange or another Republican to run as an independent, I do not know which of the following is the likelier scenario.
Note: the winner is decided by plurality (most votes, not requiring more than half).
(1) Moore’s support bleeds away to the write-in, who wins a majority (or nearly so) in the deep-red state.
(2) The write-in splits the Republican vote, and Moore has sufficient dead-end support that won’t defect, letting Jones (the Democrat) win with ~40%.
(3) The write-in attracts lots of voters away from Jones who were only considering voting for him as the not-Moore, as well as from Moore himself, such that the write-in wins, but it is a close three-way contest.
One additional consideration: it is pretty late to organize a write-in campaign, and scenarios 1 & 3 both assume that it is possible to get it off the ground, and get voters aware of what they have to do.
I still think the most likely scenario is Moore wins, and sits in the Senate (until such time as the Senate, by 2/3, might vote to expel him).