Little OT but Swiss Chard seems to grow like a weed around here. We were picking from a raised bed until early November last year. I was surprised how late it continued to produce. May grow a bit more and freeze some.
If you did not till it under it will likely come back on its own. It is a bi-annual though, so it will likely go to seed on you this year once the weather turns hot, but it will re-seed itself and next year you will have first year plants again. If you have the space to leave last years in place and plant another patch, you can always have one patch with first year plants.