Hi :)
I was just curious whether if you study web development now (and aim to master the core/essentials of HTML, CSS, JS, PHP, and MYSQL, namely) and create websites with those technologies combined, how much will you have to change re the code structure and design, in about a decade's time?
In other words, with programming being something that changes ever so often, I would like to invest my time in something that I am passionate about as well as something that won't be a great loss if I leave it off for some time.
For example, if you were to master the core principals of any one of those techs I mentioned up there within the next few months/years, what would it take to pick it up again if you left it off for some years and found that the language has changed plenty?
My father was once a PHP & MySQL expert around 14 years ago, and coming back to it now he finds the changes absolutely frustrating.

No one says a website, an app, a whatever needs to be on the bleeding edge framework.
I repeat - unless there is a need to, no one says you need to upgrade to anything new because it's new.
People still write in Fortran and Cobol. Companies still need those skillsets and companies still hire those people.
Your Javascript frameworks will come and go, every year. I "mastered" AngularJS just to have it replaced by Angular 2+. Does it piss me off that Google basically abandoned a framework and rewrote it from the ground up? Yep. Is it my job as a programmer to keep myself relevant and learn new things as they come along? If I want to pay the bills and have a good job - you bet.
And I still write in PHP - daily. I have old projects just like the next with clients that don't want to upgrade, yet. Is it hard to work on code I wrote 5 years ago? Sure, sometimes - but it pays the bills.
If you're worried about learning new things and having to learn new things - daily - I suggest a different trade. Perhaps masonry or plumbing - but even then - new techniques are learned all the time, too.
After ten years a lot of things will change, if you write a code now you should do a refactoring because the syntax will change like Javascript changing ES06, 07 and 08. But you are growing together with the technology as well.
For example, an architect builds some home modern for days today, but after 10 years new ideas, new concepts appear. So, it occurs in all areas of jobs, software development is very frequency, but it doesn't the thing for demotivating and be frustrated, the changes are important, nowadays is very nice and motivated to write an app with React instead only HTML, CSS, JS.
Keep study is the best way! Don't give up!
I've been doing web stuff for about ~15 years, and I was in college for graphic design from 2006-2009, so that was exactly 10 years ago!
As for the web technology we were taught:
- Flash: non-viable by 2010, totally dead now
- HTML/CSS: very viable, have become easier to use since then
- WordPress: very viable, has now grown to power 1/3 of all websites on the internet
I've been building websites during this whole time, and consider myself luck with WordPress getting better over time, but some things, like Flash, which were huge weren't built well, and didn't survive.
There are tons of things you could go out and learn today that would be totally dead, like Flash, in 5 or 10 years, but I know for a fact that HTML, and CSS, and JavaScript will be used, so if you look at core 'foundational' technologies, those are more likely to be 'safe' things to invest time in learning and mastering.
It's also nice that PHP is still king :D Thought your dad might be frustrated, it is also nice that he can keep building on top of knowledge he already has!
Well just one side-note about the ever changing technologies ... most of the now modern concepts are around 30+ years old. actor principles, futures / promises, functional programming is even older.
So I read the current academic papers plus some archives :) and switching a lot of languages over time (~ 1 per year) so I am not stuck with 1 set of problem solutions. It makes a lot of things easier if you at least heard them once.
The core problem will always remain the same information persistence, information transfer, information transformation/mutation.
but N != NP seems to stick at the moment and we have millions of solutions for the same problem.