There’s no guarantee the vote is lost. With the right concessions, you can ensure that any future trade deals are more.. streamlined. The governments stance was to remove freedom of movement, which goes hand in hand with the access to the trading bloc, making that concession drastically changes the withdrawal agreement and sets the base up for future relations.
Bottom line - he probably thinks that Brexit can still be achieved but with a different result - making concessions on certain issues to receive some benefits. The question is whether the government red lines are final in the eyes of the Brexiteers or if there’s room for agreement on other matters. Allowing freedom movement and retaining access to the single market would solve the backstop issue but would pose it as a very soft Brexit.
However, that would be a very Brexit lite which opens the door to Norway type deal. Which, in line with the Farages line of “taking back control” actually makes sense, unless he means borders explicitly. But given the benefits we currently enjoy, making a concession on the red lines of the government wouldn’t make for much of a difference in the current status quo, so we may as well remain.
It really does boil down to where the scales tip in favour of remain if the current withdrawal agreement is to be altered in any meaningful way to reach agreement.
Overall, I think this is a very nuanced issue and the blame that should be placed squarely on the national government is being placed on overseas bureaucracy. We’ve had all this control, just instead of voting with our minds, persistently vote with emotions and lack of foresight for the future.