Overwatering and heavy rains can cause speedwell to fail. Your cutting it down is not a bad thing; that’s recommended at the end of season, so you’re just ahead of schedule. As a perennial, it should come back next year. To help it through heavy rains in the future, you might want to work the soil a bit to ensure tha it is well draining. Ten years is a lot of time and the plants and soil may be packed it. (This will not necessarily eliminate problem in a similarly wet year but it could minimize the effect on the plants.)
Overwatering and heavy rains can cause speedwell to fail. Your cutting it down is not a bad thing; that’s recommended at the end of season, so you’re just ahead of schedule. As a perennial, it should come back next year. To help it through heavy rains in the future, you might want to work the soil a bit to ensure tha it is well draining. Ten years is a lot of time and the plants and soil may be packed it. (This will not necessarily eliminate problem in a similarly wet year but it could minimize the effect on the plants.)