If a user had 100k ada for snapshot.
They would have 100k test ada and 100k ada.
What the person did with their 100k ada was up to them.
They hopefully staked their 100k test ada. Let’s say that 100k test ada earned them 10k rewards on testnet.
That person will be able to claim 10k ada as rewards. So their ada will be what they earned as rewards + what ever their ada balance is.
The 100k test ada will always remain on testnet. And disappear if everyone shuts their pools down.
Edit. People are likely to shut their pools down as they cost money to run and there will no longer be rewards. So there is zero reason to keep the ITN pools running