The fact that you are no longer working for your old employer makes that visa invalid. As long as you are within US, your status would get adjusted automatically. Note that visa and status are 2 different things. So, you'll have to get a new visa.
The duration of stay is decided at the "port of entry", not at the time of visa issuance. If the officer at the port of entry believes that the true intention of your trip is not a visit (some people work part-time as well, which is illegal on a visitor visa), he can limit the duration of stay.
This typically is the case with many of so called "consultancy" firms. Your employer by law is obligated to pay you. You can report your employer to USCIS; and possibly seek compensation for the period unpaid.
There is a good chance that you'll be asked to leave the country.. but I would...
My cousin, who is currently on H-1B visa, got divorced recently. He realized that his wife installed some spyware on his laptop and copied all the emails sent or accessed on that laptop. Can she use these emails to report on him to immigration that he worked out-of-status for a couple of months...