Anonymous transactions will always exist, either by a service or by technology improvements.
Controlling and regulating are 2 different things and if you think governments can 'control' the cryptocurrencies then good luck, it's pure bullshits. The point of failure starts when the money hits the bank account but who told you Bitcoin can only be used with an exchange platform to convert it to fiats? If I choose to use BTC, it's not be patronized to tell me what I can do or not. Can they "control me" to buy x,y,z? Nope
As for regulating, it's a good excuse to collect more taxes, nothing more, and creating a legal framework is step 1. We were using Bitcoin for years without legislation. If it's about to say Bitcoin is legal, well BTC has always been legal (since nothing was saying it is)
Exactly. Despite government's best efforts, they won't be able to take down the whole crypto ecosystem by storm. That is because crypto is decentralized by design, greatly minimizing the risks of third parties. Still though, centralized crypto services providers are not exempt. I believe that current mixing services have been an easier target for governments because they're centralized in every way. In contrast, privacy-oriented cryptocurrencies like Monero and Grin haven't experience any disruptions from government actions whatsoever. Which is why, I believe that the best route towards privacy and anonymity would be via the protocol level.
This means that mixers should rely on the Blockchain network itself instead of a middleman or entity. We already have such solutions via CoinJoin-enabled wallets like Wasabi and Samourai. Even Dash has built-in mixing with its masternodes, while Monero enforces it by default. Zcash hides transaction information via the use of Zero-Knowledge Proofs, while Grin relies on Mimblewimble. With many diverse forms of privacy and anonymity, it'll become impossible for governments to put an end to this movement anytime soon. In the event that Bitcoin mixers become illegal, people will always find a way to preserve their privacy.
As for Bitcoin's legal status, it has always been legal like you've said earlier. I believe that government's discussion of Bitcoin's legality is more of an excuse in order to tax the whole crypto ecosystem. Most governments believe that crypto is used for money laundering and tax-evasion. While that's not largely the case nowadays, it's true that Bitcoin and other cryptocurrencies can be used for such purposes by criminals. But for some reason, they prefer Fiat on top of Bitcoin for many of their nefarious activities. In the end, governments will have to join the revolution or be left behind in the dust.
Nonetheless, I wouldn't worry too much about Bitcoin mixers as long as there are other alternative routes towards achieving privacy/anonymity. Whatever governments do with centralized mixers, will not disrupt the entire crypto industry. That's because most people don't even use mixers, leaving us with only a small portion of Bitcoin transactions on them. Just my opinion