If you applied as an FSW under category 3, you do not have to stay in Canada but if you used points for arranged employment, once you are not working anymore, you can not claim those points anymore unless you get an AEO.
If your LMO doesn't come through and your work permit is expired by the time immigration asks for your documents, you can apply for an AEO for the same job to send them instead. It is supposed to be easier to get an AEO than an LMO. An AEO will not allow you to stay or work in Canada. It is just an offer that once you get PR, you will have a job. If you are in that situation and want to stay but can't get an LMO and a new work permit, you can apply to change your status to visitor. There is no guarantee that you will get it but you may be able to stay a bit longer in Canada but without working.
Read about AEO's and LMO's here:
http://www.hrsdc.gc.ca/eng/workplaceskills/foreign_workers/supperimm.shtmlThe immigration class you are referring to which needs 2 years work experience is not PNP, it's CEC. If you had studied in Canada for 2 years and worked for 1, you also qualify. Worst case, if you end up having to go home and your FSW application is messed up, you can still apply for PR through CEC. If you qualify for CEC, your right to apply stays unchanged for a year after you leave Canada so you would not have to do it right away.