Maybe programming languages do fade away even become obscure but do they every go away? You can’t prove that they do by looking at COBOL. I found this interesting article called Cobol hits 50 and keeps counting the other day. I didn’t need to read it to know what it said though. I regularly talk to professional developers who create (and maintain but still actively create) COBOL programs. They do run as back ends and users never really see them. But they are there and doing productive work. FORTRAN is still around and used for a lot of scientific and mathematical computations. There are .NET (i.e. object oriented) versions of both languages around as well. Though honestly the idea of doing object oriented programming in COBOL scares me a little.
The first three languages I learned were FORTRAN, BASIC (BASIC PLUS specifically) and COBOL. They are all still around though they have all grown and changed over the years. I had pretty much assumed that the first language I learned after college, DIBOL was dead though. It was after all quite a proprietary language, not widely used and, well, a bit limited. I see today that it is still being sold and supported as the Synergy/DBL DIBOL compiler. It even works with .NET forms and Windows Presentation Foundation (WPF). That sure would have made a lot of the programming I did decades ago easier.
So perhaps we worry too much, if we worry at all, about the languages we teach today going away or being irrelevant when students graduate. The languages may not be as popular or as widely used for new applications but they may not go away completely. And how knows, with older programmers retiring, some of these languages may still need people for a long time to come.
On the other hand even if you do think a language will go away I think the concepts will remain. There are minor variations in syntax but the most basic concepts (loops, decision structures, mathematical and Boolean expressions and variable declarations) tend to be pretty similar across languages.
By the way, if you are interested in how different programming languages look you may want to visit the 99 Bottles of Beer project.
This Website holds a collection of the Song 99 Bottles of Beer programmed in different programming languages. Actually the song is represented in 1259 different programming languages and variations.
And take a look at the example in APL. Shudder! That one bucks the trend of things tending to look similar.
There is also the Rosetta Code wiki to look at.
The idea is to present solutions to the same task in as many different languages as possible, to demonstrate how languages are similar and different, and to aid a person with a grounding in one language in learning another. Rosetta Code currently has 272 tasks, and covers 131 languages, though we do not have solutions to every task in every language.
Maybe you will find something there that you can have your student contribute a solution for.