More than a decade ago I wrote an academic whitepaper about how I violated Twitter terms of service at scale in a way they had no method of preventing by decentralizing all of my shamelessly abusive anonymous jsonp Tweet Widget API requests across all users via a system of websockets to give me a free firehose to train ML models and serve those same users for free, and presented it at the AAAI.
Twitter presented after me, showing all the ways they were trying and failing to stop people like me. They could not do shit. It was pretty great.
I have repeatedly ignored this class of cease and desists across my career when they have no precedent for winning in court, and nothing has ever happened. These are not police. They are employees of a private company writing you strongly worded letters to scare you because they actually have no other recourse.
If you intend on engaging in a legal battle with them I would not want to participate in that money pit, but if you simply want to keep Nitter online in a way where it is unkillable, take some lessons from thepiratebay and get some cheap disposable proxy fronting VPSs all over the world that ssh tunnel or vpn back to your actual infra so your real infras IPs are never exposed. Have lots of different people run these fronting servers in a round robin pool in many different countries and legal jurisdictions to keep their legal team busy indefinitely. Each one can also distribute the load of data collection across many IPs so you technically never communicate with twitter servers at all but just run the plumbing.
I would happily run one if for no other reason than to annoy elon musk.
The problem with this is that probably you'll end up losing the domain name.
In the case of PirateBay, probably the users are willing to search for "what is the latest domain", since that's how they get their "Linux ISOs" for free.
But with Nitter, the alternative is just to go to the real twitter, so many users won't bother anymore to go find the latest domain , I'd guess. And then the project dies.