use try and catch for generic ports. The existing table will be at the resulting port
Try some generic SQL operation on your Hive (or Impala) environment. If one fails you could populate a Flow variable with some information (eg. the surviving table)
Another possibility would be to try some combination with the "Active Branch Inverter"
https://hub.knime.com/knime/extensions/org.knime.features.base/latest/org.knime.base.node.flowcontrol.trycatch.inverter.ActiveBranchInverterNodeFactory
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