as far as safety checks the query interface allows for nearly any delete scenario. For example, a constrained delete on a single index when there are multiple indicies should throw some form of exception (or simply retunrn false?) because it would result in inconsistent data across indices - that is unless the query is meant to just represent what data to delete and then its deleted in every index, but then there'd have to be a different mechanism to entire delete an index.

for bookkeeping, if all the data for an adapter is deleted it'd be nice to delete appropriate metadata, such as the adapter, the stats, the internal adapter, the adapter index mapping. Likewise if all the data in an index is deleted, similar metadata updates should occur and the table/index should be dropped.