Planted Tank Guru
Join Date: Jan 2010
Location: Contra Costa CA
Probably some have survived, dead plant leaves, snails or other livestock do produce some ammonia, and dying microorganisms (all species) will produce ammonia. Not very much, though.
I always treat a tank like this as if most of the bacteria will die off. It grows and dies in response to food supply.
If you know the livestock will not be arriving for a while I would start the fishless cycle. Start feeding the bacteria ammonia.
The test results will show you how much bacteria have survived and what you should do.
If the new fish are arriving right away, then I would buy more bacteria so there is no chance that the fish will be exposed to the ammonia they produce.
I did just that, recently: Set up a tank using some used stuff (presumably with a small bacteria population) and some new stuff. I was amazed at how fast the ammonia started disappearing. Of course the plants are helping a lot, so I do not yet know how much ammonia removal is really due to the bacteria.