every year I plant the runners that way I always have fresh plants going for the next year

Strawberries will probably last forever if you keep planting new runners and fertilize and cultivate the soil well. I got 40 new plants last year that I had propagated from one single 3-year old plant, and they are all healthy and productive this year. Even overwintered them under a thin layer of straw which was then covered by a couple feet of snow, and every single one of them survived the Zone 5 winter. This fall or next, when the leaves turn red, I will very carefully yank them all out including the runners that took, working into the soil some fresh compost and nitrogen, then replant the strongest ones, cover with straw, and thus renew the strawberry patch entirely every year or two. That is the plan. If I had more space in my yard I could move them to a new area each fall in much the same way. I do figure they'll probably last for 2 years each cycle before the soil is depleted to the point of having to pull them all and sort of start from scratch again. Except you're never really starting from scratch, you're just supplementing the soil then replanting the same plants (including new runners) every time.