Worst case scenario if the PR card gets lost in the mail, the photos aren't approved or you have no address to give to get the PR card sent to and must leave shortly after landing, you end up outside Canada without your PR card. Then you can contact the Canadian embassy in your homeland or closest to you and apply for a PRTD (PR Travel Document). This document will allow you to go back to Canada so you can apply for your PR card again.
I have never had to apply for one myself but from what I have heard, the processing time can vary from 1 day to a couple of weeks between embassies (better ask your embassy before you book your flight how long it takes, airline may not let you board the plane without it). They are often valid for around 3 months so don't apply for one if you are not planning on going back in the near future (again, ask your embassy about the details).
It should not be a big deal to get a travel document as long as you still meet the residency requirements. Since you would have to be outside Canada for 1095 days in your first 5 years as a PR before you would fail the residency requirements, it would not even be possible for you to fail to meet them if you are a PR for less than 3 years.
If you go back to Canada to stay within 6 months of your landing, you will not need to apply for a new PR card, you would simply notify CIC online or by calling that you have an address now and they can send you your PR card and it will arrive in the mail. Should take around 6 weeks. That is unless there were problems with your photos, then you would have to follow their instructions to provide new ones.
If you come back more than 6 months after landing and hadn't gotten your PR card, your application would be handled more like a renewal, that is, you would have to fill out an application, get new photos and pay a fee of $50 and then it would not be mailed to you, you would have to go to your local CIC office where you live in Canada and pick it up. The processing time now for those cards is about 4 months but if you need it faster, you can show proof of travel and ask for it to be expedited.
If you need to apply for a travel document, you can find the application and instructions here: http://www.cic.gc.ca/english/information/applications/travel.asp
If you need to apply for a PR card, you can find the application forms and instructions here: http://www.cic.gc.ca/english/information/pr-card/apply-how.asp
