That's a pretty broad question. I personally don't believe they're wrong about everything. But I also don't think the Mormons and Amish are wrong about everything either. This reminds me of a quote: “Partial truths or half-truths are often more insidious than total falsehoods.” -Samuel P. Huntington
I absolutely don't believe that JW's (or ANY organized religion for that matter) occupy any position of special importance or divine backing. My parents ask me, "Well, if JW's don't have it right, what religion does," as if to prove there can only be A or B, true or false, black or white. So I ask them who 'had it' 200 years ago. "No organized group, just a few sincere individuals trying to do God's will." "Okay. I believe the same to be true today."
But to answer your question, "What if they're right?" ...... For me, though witnesses teach God is love, it doesn't match up with his actions as described (and understood by JWs) in other parts of the Old and New Testament. He demands our strict obedience and will annihilate those who fail to seek him? When I really analyze God's actions related in the Bible, and interpreted by JWs, I find it hard to view him as a father because I am a father and I know how I feel about my kids. I am not the epitome of love and yet I could never subject my kids to many of the things that we're taught God allows to happen to people today.... for the sake of his name. Really? He's all powerful but he's that eaten up with his reputation that he'll allow these tiny, insignificant creatures to suffer to prove him right? Even temporarily? That sounds like a human. But then in order to make it all good, he sends his son to earth for - in God-time - .000000000000001 seconds and lets HIM briefly suffer and die to save all mankind, then immediately resurrects him? (Immediate in a relative sense, considering eternity.) IDK. I may have an evil viewpoint but that's not really a God I want to serve if they were right. But then, I'm kinda new to critical thinking so I haven't really figured out what I believe on a lot of things. Much to learn. So when I ask myself, "What if they're right?" it is quite unpleasant to think that my kids might have to die because I taught them what I truly believed (or what I could NOT believe). And yet that creates just one more brick of cognitive dissonance, all of which add weight to my conviction that they are NOT 'right'. So I find that question to be self-defeating.
But if I'm going to ask "What if JW's are right?" then I must ask the same question of EVERY religion out there. What if Baptists are right? (To hell with me!) What if Muslims are right? Buddhists? Jews? Scientologists? If you were raised Catholic, you might well be asking this same question on an ex-Catholic board, but about Catholicism. Truth is, all of these religions have conflicting views so they can't all be right, right? That means the majority of mankind is wrong - any way you think about it. (i think)
So my goal is to live as a good person for the benefits that come from being a good person, not to kiss the ass of one of these religions' Gods so I can get to heaven or paradise. My hope is that there is something beyond death but I certainly have no faith in such things.... only the hope that I'm wrong and so is everyone else.