Dear yellow90, work permit alone does not allow re-entry, if you are from a Country requiring visa to enter, you need to have a valid visa to re-enter. If you are from a visa-exempt country, you don't need a visa, but note that it is a risk to go out of Canada during an inland sponsorship application. If for any reason you are denied re-entry, your application will be refused. We traveled in my wife's home country last summer, before realizing we put our application at risk, but fortunately there was no problem for my wife re-entering Canada. So it is definitely possible, but it is a risk. Now, being aware of the risk, we will not travel again until she gets her PR.
Regarding the timeline, there is not much to say. We are also august 2015 applicants and no SA, no AIP, nothing yet. From the spreadsheets, we can see that IRCC is working on Dec 2015/ Jan 2016 applications. When will they work on the remaining 2015 applications is pure speculation. There is no logical reason for why they haven't finished 2015 applications and there is no way we can predict when our turn will come.