fix(flow): deal with flow drop leftover (GreptimeTeam#5391)

* fix: deal with flow drop leftover

* chore: make it warn

* chore: apply suggestion.

Co-authored-by: Ruihang Xia <[email protected]>

* chore: review

---------

Co-authored-by: dennis zhuang <[email protected]>
Co-authored-by: Ruihang Xia <[email protected]>

src/flow/src/adapter.rs

@@ -284,12 +284,29 @@ impl FlowWorkerManager {
             let (catalog, schema) = (table_name[0].clone(), table_name[1].clone());
             let ctx = Arc::new(QueryContext::with(&catalog, &schema));
 
-            let (is_ts_placeholder, proto_schema) = self
+            let (is_ts_placeholder, proto_schema) = match self
                 .try_fetch_existing_table(&table_name)
                 .await?
                 .context(UnexpectedSnafu {
                     reason: format!("Table not found: {}", table_name.join(".")),
-                })?;
+                }) {
+                Ok(r) => r,
+                Err(e) => {
+                    if self
+                        .table_info_source
+                        .get_opt_table_id_from_name(&table_name)
+                        .await?
+                        .is_none()
+                    {
+                        // deal with both flow&sink table no longer exists
+                        // but some output is still in output buf
+                        common_telemetry::warn!(e; "Table `{}` no longer exists, skip writeback", table_name.join("."));
+                        continue;
+                    } else {
+                        return Err(e);
+                    }
+                }
+            };
             let schema_len = proto_schema.len();
 
             let total_rows = reqs.iter().map(|r| r.len()).sum::<usize>();