Most probably we're staying in, but I don't think labelling those who want to leave as all being 'buffoons' is going to win any undecideds over. The fact that Vote Leave is the official campaign for Brexit should mean that we'll be seeing less Farage/Galloway and more 'reasonable' Brexiteers take the limelight.
As for what an in vote (or for that matter an out vote) means for UKIP, I really couldn't say. I certainly hope that their prospects are bleak, but what one wants and what the reality is obviously can't always be the same. That being said, I don't think a large enough chunk of people when actually voting are as upset with 'the status quo' as some angry people on the internet are, at least to me certainly not to the extent that UKIP will be getting many more MPs come 2020. There are too many unknowns to make a reasonable prediction either way, though - all I can say is that UKIP have been falling away in terms of vote %s in local by-elections since May 2015, though.