ABAP is a DSL (Domain Specific Language) optimized for developing business applications (think screw driver). Java is a general purpose language designed to address a broader range of applications (think Swiss Army knife). ABAP is vey good at one thing, Java has a broader range of applications and is pretty good at some things and not very good at others.
ABAP has been the victim of the fashion game - developers jumping from language to language to "stay relevant" and keep their cv's looking trendy. And SAP themselves seem to have got sucked into this game.
ABAP has come a cropper when it extended itself into the territory more suited to a general purpose language (e.g. PI). Similarly Java didn't look so great when used for line of business application such as SRM where a language like ABAP is a better fit.
HANA looks like it has the potential of becoming another honey trap. While there is a good case to push some functionality into the database (to improve performance and reduce the returned dataset) going overboard on push down doesn't look like good design to me, And JavaScript as a business application DSL? Given its origins I'm not convinced.
ABAP will stick around for the same reason as COBOL. It's a good tool for a particular type of job and a good engineer will always choose the right tool for the job - not the shiniest.
So my advice would be learn what the tools are good at, decide what type of work you want to do and choose the right tool for the work at hand. Tool hopping may help in terms of understanding what is possible but it doesn't encourage a deep understanding. Better to accept going out of fashion so that when the dust settles and business starts to look beyond the surface you have the advantage of some substance behind your cv.
You never know - we might even end up with some better engineered business applications as a result.