The O-1 class of visa is also an option, no prevailing wage requirement. So that is more attractive for a startup employee/founder. But you have to meet the "outstanding" requirement. H1B and O1 apps cost the company applying approx $5000.
A co-owner can be sponsored for an H1-B. I have seen it done. But you have all the normal H1-B issues e.g., prevailing wage. Also the word from immigration lawyers is to expect it to be much harder for small startups to get H1-Bs for any of their employees this year ... very bad news.
Seems to be a lot of confusion here. If you fail to meet the requirements after two years - you don't get kicked out of the country. You just can't get a green card via this method and you will need a new visa. If your start-up is still viable you could try to get an H1-B etc through it, or go get yourself another job. All visa holders are used to this kind of precarious situation already - loose your job, drop/get kicked out of school etc and it does not matter how long you have lived here, how much property you own, how many US degrees you have, you are on a ticking clock.
Startup visa is a move in the right direction - it adds another viable path to permanent residency. A path other than joining a big company and relying on them for example.