Yeah - without the shortfall being covered by a retailer (such as HTS, Amazon, Target, etc...) if there are only 4999 backers at midnight on April 4th, that's it, the item does not get made.
I do find it highly unlikely we will end up in a situation where there will be less than say 20-30 backers to go though. Anything less than that, I'm sure HTS can afford to step in, pick up the remaining units and bring 5-10 of them to events like SDCC or the next SWC and unload them pretty easily. And I wouldn't be surprised to learn that there is a contingency plan in place if they do get that close. Better to do that and maybe even eat $5k - $10k worth of product vs. having it end up a failure with less than 20 backers to go.
The good thing about this is that it does show viability for the concept at this point - here's hoping that they already have a lower price-point item on deck.