If the opposition rams through a second referendum with the options of "Remain" and "May's Deal" before the election the brexiters could just boycott the referendum. "Remain" would then win with a 99% share and the referendum would have as much legitimacy as the Northern Ireland referendum of 1973 where the unionists won with 99%.
They should have "Revoke Article 50", "Bypass Parliament and Agree to the currently agreed on negotiated separation", and "Leave and Default".
If no one option gets 50%, they should then have third referendum with the top two choices unless parliament passes one of the top two choices.
What do you think would happen in that case?
Personally, I think there should have been a second referendum on ratifying the deal once it was struck.