My uncle lost his in Koh Chang, he filed a police report and had to go to the embassy to get a temporary passport. So make an appointment with the embassy ASAP and get there with a few passport photos and a police report and that's it.
Ho Chi Minh is fine. Garret hasn't been there and doesn't know what he's talking about. I went there to get a non o , year long multi entry. Everything was fine. No queues no questions no problem. Went there on the Thursday afternoon and was seen instantly and came back on the Friday with no queue whatsoever. Good luck on your trip mate. Keep your wallet stuck to you like glue tho !