If the system has been properly filtered,there is no food for mold in the ducts. The duct has dried out after a month so if there was a possibility of mold,it has passed now. The area in and around cooling coils stay wet the intire summer under the best of conditions anyhow. If the heat or cool was used after the flood,the ducts were at the same level of moisture within 72 hours as they would have been before flood. I see no reason for concurn but if you want reassurance,mold test kits are inexpensive and available at most retailers.

return is not the only area where voc's enter ducts.
unsealed cuts in supply plenum for duct take offs,
plenums not sealed to equipment
return air & penetration of supply box into
living space all need to be mastic sealed.

has anyone opened any ducts since the flooding?
for water to get into the ducts..they are not
mastic sealed completely.
taking a look into the ductwork is where I'd start.

hard pipe or flex duct?

best of luck.

My HVAC company came out the following day to inspect my system and did drill into the ducts and did not see any leakage. I have scheduled a duct cleaning company to come out next week and they will sanitize the ductwork. He feels that any water that was in the system dried up, evaporated over time.