SMT is all that is in production design these days isn't it? Very rarely do you find TH components unless it's a crystal or "special" component.
Anyway, every IC has a chance of obsolescence, my last nightmare was the EXAR 2206 monolithic function generator IC,someone may has well have been prodding me in the ball sack with a sharp pointy needle for all the pain that caused!
But with modern technology taking over, I was able to perform the same function with a PIC within the same package size and almost same layout.
So you can't say that they will never remove a chip from their line, they have no real justification either (not that it seems they need to justify it), you can't say it's solely because of lack of demand because there was uproar in the community when it was removed, but it has been around 20+ years etc etc.
The 8051 is still used today, some modules for things like ISM Radio, WiFi, BlueTooth, etc use a Turbo 8051 core, and the Keil and IAR compilers etc are still available for the chips.
If you are going to use it in a project or product and you are worried, I would say do what I did with the 2206 and buy a shed load from a component sourcer and store them! Don't forget spares!