Hi As per my experience and conversation with CIC agent.
you can go head apply your new open work based on nomination. Don't tell them you got fired. You can apply right way.
Yes you can apply open work permit but during determine eligibility you have to select answer yes for question Permanent Resident first stage approved. After that it will not ask you Letter of support.
My timeline under EDS:
Application received: 09-October 2014
File Number: 04-November 2014
NOC : 0621
W/P expiring: 15-October 2016
Call/Nomination: still waiting?
Please update who applied in September 2014.