I think strawberry plants are fairly short lived as it is. I think (this is based on my experience and some reading, so take with a grain of salt please!) that strawberries are mineral accumulators and once they have mined all they can from the soil, they begin to fade a bit; however if grown in a polyculture, with lots of renewed organic matter from leaf fall, added mulch,
compost, etc; and with good soil biology, they should be able to continue for longer. But I also believe sending those runners out is a way of helping get the offspring to move to a more mineral-rich place than the parent plant.