1. A system, comprising: a plurality of computing nodes, each comprising at least one processor and memory, wherein the plurality of computing nodes are configured to implement a data storage service, wherein the data storage service comprises: one or more replica groups stored among the plurality of computing nodes, wherein each of the one or more replica groups maintains one or more replicas of data on behalf of one or more storage service clients, wherein each replica group of the one or more replica groups includes a healthy state definition for the replica group; a replica group status sweeper, configured to identify replica groups with a number of available replicas not compliant with the healthy state definition for the respective replica group, wherein said identification is based, at least in part, on status metadata for the respective replica group; and a dynamic heal scheduler, configured to schedule one or more replica healing operations to restore the number of available replicas for the identified replica groups to the respective healthy state definition for the identified replica groups based, at least in part, on one or more resource constraints for performing healing operations