If a text extraction is blocked (weird PDF) or a blob cannot be found in the datastore or any other error upon indexing one item from the repository that is outside the scope of the indexer, it currently halts the indexing (lane). Thus one item (that maybe isn't important to the users at all) can block the indexing of other, new content (that might be important to users), and it always requires manual intervention (which is also not easy and requires oak experts).
Instead, the item could be remembered in a known issue list, proper warnings given, and indexing continue. Maintenance operations should be available to come back to reindex these, or the indexer could automatically retry after some time. This would allow normal user activity to go on without manual intervention, and solving the problem (if it's isolated to some binaries) can be deferred.
I think the line should probably be drawn for binary properties. Not sure if other JCR property types could trigger a similar issue, and if a failure in them might actually warrant a halt, as it could lead to an "incorrect" index, if these properties are important. But maybe the line is simply a try & catch around "full text extraction".