There is no requirement for your employer to pay your airfare to Canada, if they do then thats a bonus for you, but not something you should expect. However, if for whatever reason they can't uphold their duties and their designation from the program is revoked or they can no longer keep you on and work with the province to find suitable alternative employment, they may be required to cover your fare home. Fingers crossed it never comes to that.
If you are granted a work permit via this program, you're allowed to work in Canada for that employer prior to PR. Work permits are only useful when you are not a resident, once you have PR you do not need a work permit.