Sounds like a pretty straight-forward plan, right? Especially in lieu of ad-based models becoming less feasible for webcomics, and the challenges inherent in trying to distribute relatively low-run print books through Diamond. If you can't do either of those, you just throw it up on Kickstarter and you start seeing what amount to guaranteed sales.
I mean, sure, you kind of know that not every Kickstarter project gets funded, but it's not going to happen to you, right? After all, you've got friends on social media and you got some really good feedback from that other book you were selling at a convention last year.
But it not getting funded is a real thing that happens, though. Regularly. To a lot of people. So what do you do when you become one of them?
The first thing is to look at what happened. Kickstarter gives folks access to a lot of good metrics, so take advantage of them. What reward tier(s) were most popular? Which ones were least popular? When did most backers pledge to your project? Can you tie that back to something you did -- a Tweet, a convention panel, an interview..? For that matter, do you know who backed your project? Was it just people you know, or were there a bunch of people you'd never heard of before? And don't forget to check out the comments! Did people leave feedback about either your concept or the KS campaign? What recommendations/suggestions do they provide?
Jim McClain tried to run a Kickstarter for his Solution Squad comic back in 2012. It wasn't funded. In fact, it only got 14 backers who only raised 7% of the target. Part of McClain's problem (and I've talked to him about this since then, so I know he's aware of this and is comfortable talking about it) was that he tried getting the attention of "traditional" comics fans and press. The same people who were interested in the X-Men and Justice League.
What he realized, though, was that wasn't his core audience. His comic, which is heavily focused on math and helps students to learn sometimes tricky subjects, goes over much better with teachers, who see the educational benefits. So by catering more directly to them, with reward tiers that include library copies and teacher in-service visits, he's doing much better with his new Kickstarter. As of this writing, it's not completely funded, but he's already over 70% there with over three weeks left! That's no guarantee, but it's a darn bit more impressive than his first go-round.
My point here is that a failed Kickstarter might not be a reflection on your core concept, but your execution of the KS campaign itself. It's possible your idea is just crap and nobody likes it, but it's also possible that you're just going about Kickstarter the wrong way!