So Nicola Sturgeon today repeated her hint of a few weeks ago that the SNP would be prepared to install Jeremy Corbyn as Prime Minister on a temporary basis to prevent a No Deal Brexit. Of course SNP, Plaid and Green support wouldn't be quite enough to give Corbyn a majority - he would also need the Lib Dems and at least some of the ex-Labour or ex-Tory independents. But the intriguing thing from a constitutional point of view is that he wouldn't actually need to win a majority in a parliamentary vote before becoming Prime Minister - the Queen could appoint him and see if it works out, which is essentially what she did with Boris Johnson. What circumstances she would do that in are unclear, but if Johnson was to lose a vote of no confidence, SNP support could leave Corbyn as the only game in town.
On the other hand, if Jo Swinson does prove able to block a Corbyn premiership, history may not be kind to her, especially if a No Deal Brexit is the outcome. What I truly don't understand is why her focus is on keeping Corbyn out rather than getting herself back into government in a senior position. If the SNP decide to support a Corbyn-led government from the outside, Swinson would even have a claim to be Deputy Prime Minister, as long as she could accept Corbyn as PM. That's how governments of national unity work - not by exclusion, but by inclusion. Intra-party "dream tickets" work on a similar basis - for example, Kinnock/Hattersley or Blair/Prescott.
Another possibility would be the model briefly tried (not terribly successfully) in Germany in the late 1990s, whereby Corbyn would remain Labour leader and would hold a very senior position in government (such as Chancellor), while someone else becomes figurehead Prime Minister with his blessing. But really, any temporary government in which Corbyn is not the dominant player is a non-starter, and if the Lib Dems are remotely serious about stopping Brexit, it's about time they woke up to that.