You can apply to restore your work permit in the first 90 days after it expires. If you do this, you can stay in Canada until you get further instructions, but you must stop working until you receive your restored work permit. There is no guarantee that your application will be approved.
Otherwise, you must leave Canada right away when your work permit expires. If you do not leave, you could be deported and will need permission from an immigration officer to come back.
To restore your work permit:
send an Application to Change Conditions or Extend Your Stay in Canada as a Worker to the Case Processing Centre in Vegreville, Alberta,
on the form, say you are asking for your status to be restored and your work permit extended, and explain why you stayed in Canada longer than allowed, and
pay C$200 to for your status to be restored and C$150 for the work permit itself (for a total of C$350).