I wouldn't say it's impossible for the usd to be highly devalue but as long as economic keep moving, that can't happen. Check back from 2008, we keep hearing dollar will collapse but its getting stronger with little inflation in my opinion. USD may have inflation range of 2% as predicted by some analyst because interest rate still remains 0 and stimulus distribution is still on check.
Bitcoin isn't backed by usd, it's just a value that is determined by the market force, its independent of other centralized bodies( in the past) but currently correlated with stock market( S&P 500).

Bitcoin is bitcoin, demand and supply is the key factor that driven it's economy which has been working perfectly base on Satoshi whitepaper. All eyes are now focus on US elections, thus Bitcoin is enjoying  the news. We have seen how PayPal, one of the giant payments system across the world is adopting cryptocurrency payments on their, that's how decentralized it should be and not tide to some individuals decisions (S&P 500 and Gold in traditional market for example).