Go for the degree. If you ended up with a Senior role then you have lots of experience already, I assume. You'll ALWAYS be able to find another job. With a PhD in Crypto, you'll be able to move towards a Crypto job, or teaching if that floats your boat.
Side note: I am very jealous and a bit inspired. Former military and my academic route is mangled with starting late and working full-time as a developer, and so I'm hoping to complete a bachelors by 28 or 29 at my dismal pace. The fact you 're looking at going back to school at 30 for a PhD makes me feel like it will all work out one way or the other.
Ten years from now, it may become difficult to choose a PhD. It may have far less financial impact if one has developed deep industry experience. However, even so, a PhD will still create wider opportunities for changes to other markets and career tracks.
When your kids enter college, going back for a PhD may become unthinkable.
Why did you always wanted to have a PhD? Do you want to work in research or academia?
I want to go to academia because working for companies and fixing their immediate shits doesn't make sense to me. I can't do what should be done. Have to always serve the boss. I want to be in a place where I learn and whatever I publish be of some value. Not just another software or another web application.
I think 10 years after. After 10 years , I don't want to be some manager/lead of some X company working under some boss. I want to be an expert in some field, distinguished and want to have my own identity not just X number of experience is some company.
I want to do research, valuable work.
For a more pragmatic point of view, look at where your future professor's students are. In a 250+ ranked school, the school name is not going to land you a great job by default. You'll need to be working with a good professor. Your summary of the publications of who you are working with doesn't seem stellar, but without details on where he publishes I can't say much. How many students does he have?
Do you have only that one offer or more?
This is the only offer I have.
Is the PhD in the US, Europe, or somewhere else?
As for government funded: you also get a monthly stipend, right? How long is the PhD in your country?