That is correct, the bandwidth and disk space would just get added on to the total amount allotted for your account. As long as you didn't run out of bandwidth then the files and transfers would remain running. The transfers themselves get auto-removed after you run out of transfer, but the files themselves would remain in your cyberlocker for at least 30 days.
Now that you put forth that scenario, I do see how the disk space could become a problem if someone is just hoarding their seedbox transfer. I will have to give it some thought and come up with a way to prevent that from occurring, but the most likely obvious solution will be to implement a time limit on paid accounts. This way after X amount of time (6 months?) a paid user will get reverted back to a free account and then the timed limit on files would apply.
We're still in the pretty early stages of development, so there are lots of things we're still working out. If you have any suggestions please feel free to share and we will definitely take them into consideration.