If I use my EAD to work in B company for two months,can I return A company without doing anything for the H1-B which was sponsored by A company?
-Technically, if you use EAD to work, you lose your H1 status though USCIS can not tell it by this time. But you can not be risky. So, I sugget you to go to outside US to get an H1 visa to come back to re-instate your H1 status.