I have a flight home to Canada booked out of Beijing but will be flying into Beijing from another co

I have a flight home to Canada booked that flies out of Beijing. I have a Chinese visa but will be leaving the country for an extended period before coming back into China to catch my flight to Canada, making my visa null and void. Do I need another one if I am not leaving the airport? The flights are with different airlines and my baggage would not be checked in Beijing so I would have to leave security to re-check my luggage.