The data remains on the drives. When you add the drive(s) to a pool no formatting takes place. Just make sure that the data is already part of a share folder first.
You can see the drives listed individually and they are annoted as pooled drives under a seperate drive letter when added to a pool.
Just remove the drives from the pool before uninstalling drivepool and you should be good to go.
Just be aware that you will not be able to use duplication at the moment if your drives are that full. It's just a fancy name for mirroring in the long term.
I've just started using it with a mixed bunch of drives and it looks good so far
PS
I meant to answer before when you posted this question in another thread but got waylaided by work etc... sorry for the delay
EDIT
I'll try to post a screenshot from my dashboard for you to show what I mean... but will be delayed for a while. Away from home and I do not Remote access set up at the mo