I'm sorry to hear that. Unfortunately, the Green Card sponsorship process is way more involved (AFAICT) and with much longer time-to-completion. I'd personally find it hard to believe that a startup would be able to take you through the whole process, given the probability they're out of business within a year or so.

Similarly, once you start the Green Card process with an employer, you aren't likely to go through with an H1-B transfer. It's a broken system...