The last one is tricky because who is going to sponsor a worker at the price tag of 100k with no guarantee of performance. That is rife for abuse. You could get google to sponsor you and then hop to your friends startup on day one.

It is reasonable that if you get a temporary visa to perform work in another country, and you decide you don't want to do that work anymore, you leave. They aren't enslaved or anything if the work is not worth it you can attempt to transfer your status to another employer or leave.