Either your colleagues have a better crystal ball than me - or more likely - they're guessing. The fact is no one knows what's going to happen the in future. I can't tell you what jobs will or won't be available because it's unknowable.
That said, in my opinion there will still be new and exciting PL/SQL jobs for many years to come. It's a core component of the Oracle database and APEX. People are building plenty of new APEX apps. See the following for some examples:
https://apex.oracle.com/pls/apex/f?p=411:5:::NO::: As I'm writing this (Sept 2015), the TOBIE programming language index shows PL/SQL up two places on last year (from 20 -> 18):
http://www.tiobe.com/index.php/content/paperinfo/tpci/index.html PL/SQL was also a key component of actively developed applications in the role I left last year. So I think there will be PL/SQL jobs for the foreseeable future.
There will be new jobs using Big Data technology. I doubt this will have a significant impact on the PL/SQL jobs available however. It's still a relatively niche area that's not relevant for many applications.