I'm willing to bet that it won't be Heather Roy. Whatever role the pro-Roy factor may have had in The Fall Of Garrett, she'll always be seen as the person who had most to gain from it, and thus will be rejected. No-one likes to reward treachery.
John Boscawen might be the obvious choice, but I suspect he'd be reluctant to take the job, for reasons idealistic and cynical. Idealistic, because he's probably bright enough to realise that he won't be able to save the party. He hasn't got the profile of Hide, or the charisma of ... well, anyone, really. The cynical reasons are that he's probably bright enough to realise that no-one will be able to save the party, and his future probably lies with National. He probably doesn't want to be forever associated with the demise of ACT.
Likely incoming list MP Hilary Calvert is obviously out of the picture. Parachuting a neophyte list MP into the top job in a party would be just be ... silly. So perhaps we shouldn't right that option of entirely. It is ACT we're talking about, after all.
Which leaves Roger Douglas. No, don't laugh. It makes scarily good sense.
First of all, he's got a political pedigree stretching back to the 80s, and has held high office.
Second, he's got name recognition that none of the other potential candidates have. The rest of the party are non-entities, Roger Douglas is, at least, a somebody. People know who he is, and recognise him as
that bastard from the 80s we all hoped we'd never see again a significant political Somebody. Compare that with Whother Roy or John Boscwhoen.
Third, he might just have the gravitas and reputation to either scrap ACT up to 5%, or (rather more unlikely) win an electorate. With National probably intent on squashing Hide, that's probably an essential consideration for the others.
Fourth, and probably most important, he doesn't want the job. He doesn't even really want to be in parliament, so his elevation to the leadership would always be temporary - probably, to try to get the party back into parliament in 2011, followed by graceful resignation of the leadership. By then, the bloodletting between the populists and the purists will have ceased, and they'll be willing to make a rational choice about who is to lead them to oblivion.
And if oblivion comes in 2011, then who is better suited to be the captain going down with the good ship Libertarian Delusions than Roger Douglas?