This is likely a dumb question:
If you kill the cancer cells, do you stop whatever is causing them to be created, or more to be created?
You just kill existing cancer cells. That means they won't multiply and become exponentially more cancer cells, which is what tumor growth is about.
Of course you don't stop normal cells from turning into cancer cells at some point. Because even if they are able to "tag" cancer cells, they likely wouldn't be able to tag "normal cells that are gonna turn into cancer cells a year from now". So no, cancer could presumably always come back. But one might hope that, 99.9% of the original cancer having been swept away, your body's immune system - and perhaps more RF treatments - would suffice in controlling what remains and what shows up later.