I can't provide any 'proven facts' about healing. That's not a subject we'd ofen raise to disprove JW doctrines.
To try to argue with JW's on something they don't believe (Trinity, charismatic gifts, hellfire) usually gets you nowhere. It's more straightforward to get them on things they actually do believe in (such as the 1914 doctrine, other dates they had to change). Even then, it's usually hard to get through to a JW.
Usually they only see the light about their organization when they're ready to, and it's usually more over the lack of love inside their Kingdom Hall than it is over a particular doctrine.
Hrmm. The thing is a good friend of mines spine was healed at a worship thing. Every week i have some JWs come over (every tuesday) and we just talk about beliefs. one thing i stumbled across was him saying that healing by someone who believs in the trinity is satanic. Now if they believe that satan heals, thats a kingdom against itself, which cannot stand according to jesus. if they dont believe that satan can heal, then The holy spirit was infact the healing force, and they spoke out against it. Now im not saying they're unforgiven, because they most likely have to witness it and then speak against it, rather than just hear about it. but im worried what JW's will do if they ever witness one.
another thing is they dont believe that it wasn't all jesus that did the healing, but relied greatly on the healed persons faith. Jesus always asks "do you believe it can happed?" and they would say yes. he would then go to say "then it is done". Never did he heal a person who didnt believe it could be done. the bible even says somewhere "and he didn't do many miracles there because of their lack of faith. it was funny watching him change the topic immediately when i informed him of that little detail.
i dont believe any denominations are 100% correct. They just seperate people who love God. I'm sure there are people who are JW and people who are other denoms that are on the right path to Christ.