When history beckoned, Jo Swinson was caught napping. Or more accurately, she was caught posturing about things that didn't really matter. (Such as the identity of an interim PM who would have been in power for an extremely short period of time.)
Secondly, the outcome of the forthcoming election may be affected by the Brexit Party's decision to view the deal as a betrayal. If the deal is rejected tomorrow, and an extension is requested and granted in line with the Benn Act, and then Johnson seeks to win the election on the promise to get the deal through, it seems likely that the Brexit Party would put up a full slate of candidates against the Tories - which paradoxically could mean that Johnson's negotiating triumph will make it harder for him to be re-elected. The same would apply if the deal is ratified before the election. The only way Farage will back off now is if the deal is rejected, the EU refuse a further extension, and a No Deal exit actually occurs before the election. But I think that's pretty unlikely. The EU may try to force MPs' hands by making noises in advance of tomorrow about refusing an extension, but will change their tune if the deal is voted down.
Mind you, it may not matter to the Brexit Party's electoral strategy whether this deal is passed before the election, but it certainly matters to the Liberal Democrats. If Britain has already left the European Union by polling day, the clarity of their "stop Brexit" message will be spoiled. They'll probably come up with an alternative message of negotiating as close a relationship with Europe as possible, but that may not capture people's imaginations in quite the same way. The SNP will have no such problem: they'll still be able to inspire Remain voters with a crystal-clear pitch of swiftly rejoining the EU as an independent country.