Labour will say that Tory Brexit does not deliver on Keir Starmer’s 6 ludicrous tests & will advocate #PeoplesVote. First signs already emerging for this from the party = champions of successful 2nd referendum.
Tories will lose voters who wanted hard Brexit (no ECJ, stopping of Freedom Of Movement) to re-emerging UKIP or similar party while Labour can claim to have softened Tory #Brexit = Labour gaining majority
Labour would vote against this in parliament (6 tests) but might not be successful in stopping it. Labour will be seen as the ones who warned & would have delivered the better Brexit = Labour gaining majority.
As per scenario 2 (Soft Brexit) voters desperate for hard Brexit will seek alternative party to the Conservatives - Tories will lose majority even with DUP. Labour gaining majority.