Manually modify master-bin.index
The best advice would be to rebuild the slave. Missing 8 binary logs means you may be missing a lot of transactions. Another option would be to execute CHANGE MASTER to and move to the next available binary log. You may need to skip slave errors along the way until the slave 'catches up' BUT you have to use pt-table-checksum and pt-table-sync to "resync" the data between these nodes.