The re-entry permit is issued until the final date of the current visa. If it's a normal education Visa that means it's every 3 months. If it's a university program it's usually one year. But without seeing the passport you will know when it expires. If you're not back by the date that it expires your education Visa finishes.
It's probable that a regular 3 month extension visa will finish soon, so try to extend early.