Python? Good luck. Every frigging month (practically) it's a breaking change. You have to work furiously just to keep your infrastructure working, or purposefully draw a line in the sand (2.7!).
I run Fortran every day (via NumPy and other packages), and some of us are investigating just switching to it for some projects (we need the math speed, and all the C++ matrix libraries involve compromises of one form or another). There's no reason I and my peers wont be doing the same in 50 years. It works, its fast, its debugged, and it is easy to use things like Python 5000 (by then over 70% of people will have made the transition from 2.7 to the 3.x version!!!) to do all the glue work that Fortran is not optimized to do.
Fortran codes ain't ever going to be a liability[1]. Python 2.7 on the other hand...
[1] because of being Fortran. Poor coding style was endemic in Fortran77, and that can be crippling, but to a large extent that is language agnostic. I acknowledge the required short variable names of 77 doesn't help, but people would not comment what the variables mean, and that is the real problem (IMO). Poor structure is another problem (masses of gotos). Yes, 77 doesn't make your life easy there, but discipline is possible. We can quibble about all this; my point is the 'modern' languages are going to be old quite soon, and we will face real porting problems then. Move 20,000,000 lines of JS and Python? Good luck.... Get a Python 2.4 code base working with 3.9? Ah, hmm, well .....
But Fortran? We build it and run it every day, easy peasy.