There’s a lot to disagree with in this post, but: the first link in evidence that “most lawyers agree” that an exit payment is legally required doesn’t say that at all. It says there is legal uncertainty, and reports (as is well known) that the EU’s position is that there is an obligation and the UK’s position is that there isn’t. At best “most lawyers agree” is mischievous; at worst a downright lie.
Later you castigate Hobolt and Leeper for their inclusion of the “no payment” choice (which is an essential part of the “no deal” strategy they wanted to include in the option set), and not to include numbers in the £36bn-£100bn range discussed in the newspapers. But these figures are demands speculated by the European Commission; it simply isn’t plausible that the UK will pay £100bn, for political, economic and indeed political-economy reasons.
That’s symptomatic of the whole piece: an insistence that the “no exit” option should be considered in the poll and that only the terms proposed by the European Commission are feasible, and no others should be polled.
Hobolt and Leeper’s choice to ignore “no exit” but to include options such as “no payment” and “all must leave” is justified because they are within the option set defined by current British political discussion, including the government and the main opposition. There is no meaningful political option to stay in the EU (the Lib Dems stalled at the general election), and there are circumstances where EU intransigence would provoke a breakdown of negotiations.