Hi sophisticate,
No doubt, an unfortunate turn of things at the startup. Such upheavals do happen to people at one or the other point in their careers.
Here are my thoughts on the issues you’ve raised:
1. You know that IBD is a rather unforgiving industry in terms of work hours. Meet few of your friends who’re working there, and besides asking about the industry, prospects, good things etc., also ask what are the things they dislike. The obvious one is long hours, but there could be other things as well such as work culture. (I interned in IBD, and culture was the biggest turn-off.) Do it thoroughly this time because you won’t want to have another U-turn. It’s hard to pinpoint an industry that will work for you, but you’ve to match your strengths & weaknesses with the industry, and see where you’ll be more natural
2. I agree with Scott that one year is nothing in the larger scheme of things. Don’t fret over it. I wouldn’t worry even if it’s two years.
3. I don’t know if you’re planning to apply to B-schools this year. Although your workex is on the lower side, I would say go for it if you aren’t finding good job opportunities. You’ll find plenty of opportunities to consider once you’re there in a B-school.