The key to all this is the Alabama Republican Party. Alabama voters aren't being asked to directly elect Roy Moore to the Senate. They are being asked to elect the nominee of the Republican Party of Alabama to the Senate. The Alabama GOP is a private organization, that can choose to rescind its nomination on the basis of its view that a creep harms its reputation.
This is all acknowledged by the Secretary of State of Alabama, who said yesterday that if the Alabama GOP withdraws its support for its nominee, and Moore still wins, the election will be declared null and void. The implication is that if Moore were to drop out, and still win, the election would similarly be declared null and void.
Fast action is required, because if either of these scenarios can be effected, pressure can be brought to bear on the Governor of Alabama to support postponing the special election so the GOP can run a new nominee (maybe even Jeff Sessions himself).