So is there any lingering possibility that a referendum might still not happen? Yes, but that outcome is looking less and less plausible. It seems to me there are only three conceivable ways in which a independence vote might be averted -
a) The advance briefing of Theresa May's speech tomorrow might not match the eventual content, in which case there may still be an outside chance of the UK remaining in the single market.
b) EU leaders might do a highly improbable U-turn and drop free movement of people as a precondition for continued single market membership.
c) Theresa May might do a highly improbable U-turn and agree to consider special status for Scotland within Europe after all.
Of those, only a) seems remotely credible. In which case, an independence referendum might start to look all-but-inevitable as early as tomorrow.