I suspect that the reason they've gone for an Election Bill rather than an FTPA election is political, rather than logical. As long as Johnson used an FTPA motion he could be defeated again and again, making the point that he served -- as he does -- at the discretion of the House, and not the other way round. With a Bill, though, Johnson doesn't need Labour support, and so they are more or less obliged to support it now, but with the pretence that it is on their terms not his.
The Labour leadership has got this wrong. There is clearly no material difference between an election on 11th December and one on the 12th. In that sense, if they objected to the 12/12 they should continue to object to this 11/12 one. It's manifestly nonsense to argue that the two positions are in any way consistent.
As to the question, No Deal can't be taken off the table permanently, but it should be clear by now that it is the "default" in name only. The EU does not want No Deal. Parliament doesn't want No Deal. Even Johnson doesn't want it, really -- but it served his purposes to pretend that he did. Therefore, No Deal simply cannot happen merely by default. Unless one or other of those bodies changes their minds, or is replaced by people who *want* No Deal, then this will always be the case. The UK will either leave the EU with a Deal, be it Johnson's, May's, or some other version, or will not leave at all.