If anything was going to finish off the JWs, it would be apathy.
That fact has been noted by many others who contribute on this discussion board, and is certainly recognised by the JW leadership. (Over 30 years ago, I can recall the Circuit Overseer doing a rant about how apathetic we were all becoming. I have little reason to believe that much has improved since then!)
In the JW world, one thing gauranteed to counteract apathy is an outbreak of persecution. So much so, that it was often noted that in the places where the JWs became legalised, there then began a slow but steady trend towards apathy.
Trying to ban the JWs may inflict some harm on them, but would likely be more than offset by the shot of adrenaline that it would subsequently release!