Regarding individual travel plans - yes, this is how most "single trip travel insurance plans" work. It has to be purchased before the trip, and coverage ends when the covered period ends or when you return back, whichever is earlier. When you buy 180 days coverage, some plans would also require you to wait 1 month before purchasing another 180 days coverage. Keep in mind that BC MSP will cancel your 1-year exemption (which can be as long as 2 years), if you return to BC for 30 days or more, because they will consider then that your year-long trip has ended. Some travel plans allow incidental trips back to home country without interrupting the coverage, but it has to be "incidental", i.e. your intent is to continue the trip and leave the country soon again.
There exist such thing as "Annual travel insurance". Most companies have such a plan, it allows unlimited number of trips, you leave and return whenever you want, and remain covered in any of these trips, though the duration of each trip is usually short, like 30 days.
Though sounds like you already have a group plan of "annual travel insurance" variety, covering short trips.
There are also some VERY expensive annual plans that will simply cover you all year round all over the world, including your home country, no matter how long you stay where. Check IHI BUPA for example. Very expensive.
BC charges for health care plan mostly those who can afford. People with income more than 30K per person pay $69 a month (was $66 last year). As the income gets lower, so do the premiums, and people below 22K per person don't pay anything.