I've attached a patch for the following classes:
and the example search request handler configuration:
To see this patch in action, apply it at the solr root and run "ant example". Then follow the distributed search example instructions (http://wiki.apache.org/solr/DistributedSearch#Distributed_Search_Example) to get two Solr instances running locally. Run the curl command to search across both instances. Stop the instance that's listening on port 7574 and re-run the curl command. You will get a search response containing a header that reports you've got partial results, as well as which shard failed.