Although I'm not familiar with
Comodo's sandboxing,
I think the principle is similar to other forms of containment.
I'm using Sandboxie now. This essentially means that unless you have recovered an infected file or app, & already run said file
outside of the sandbox, your system should remain un-exposed, unchanged, & thus safe.
Deleting the contents of the sandbox flushes all un-recovered files away which should leave your system's state unchanged.
Even new additions such as extensions & extracted software programs run in a sandbox should be safe. Any pre-existing infections cannot be helped by containment. I hope this helps.