Thether does not collerate with bitcoin's price, though. It collerates with USD (fiat) and always maintain it's 1:1 ratio. In short, even if USDT disappears, BTC will still maintain its value since it has a comparative value in USD (fiat) and other altcoins (e.g. ETH, BNB, XRP, XLM, etc). However, I do think that any stories about USDT being a threat to BTC are just mere speculations and theories that might be created by BTC non-believers and those who are pissed off of themselves for not buying BTC when it's still 0.01USD. Those people will always be a laughing stock of the crpyto-world (e.g. the man who bought pizzas for few BTCs). There's a lot of conspiracy theories that appeared about BTC, but none of those have stopped BTC in reaching the $40k mark.