I think one option would be to check the kickstarter site directly. I am sure nowadays they have a faq in terms of tips and recommendations, as well as guidelines of what you actually have to have ready when making a project there.

My personal opinion (with zero experience on this, mind you) is that I can see it being difficult to pitch something without showing anything. Ideas on text are usually not enough. I would want to say 'nowadays' because of so many games out there, as well as failed kickstarters - but honestly I believe it would never have been too easy without some material to show. Of course there are always exceptions to the rule, but I am sure you can see how small that chance would be.

That being said, if you already have 25% of a demo, do you not have anything to show? At least anything from the project, or maybe to underline your presentation text.

At the end of the day: If you set up a kickstarter that gets cancelled/refunded if it does not meet the goal, you at least tried. (I believe that is how it works, right?) Others even tried a second time afterwards. That being said, this could harm your 'publicity' (or basically said, a second run must not always work out great).

In regards of what you should do: Difficult - as is the whole Kickstarter affair. I just recently looked into a project where the dev did a successful second run on it - and they pretty much regretted their decision because of what it meant to work on the game under that circumstances. But that is only one possibility.

My recommendation: Check the kickstarter website. Ask for advice (as you did). Think about it from all sides and what you feel would make sense in your situation.

That being said, anyone clearly having more experience with this than me should feel free to chime in on this.