What will kill arrangers as they currently exist is the death of the user base (old fogies) which is inevitably happening.
I sure hope not. In 20 years, my 53 year old son will be an old fogie, same with my 49 year old daughter. What categorizes an old fogie? Old fogies will be around till the end of time. With luck, everyone will eventually become one - I did, though I've been playing an arranger keyboard since I was in my late 40s. For me, it really changed my musical life and I suspect that will be the case with anyone that decides to delve into the inner workings of an arranger keyboard as a serious musician/entertainer.
Up to that point I was a singer/guitar player with a 5 piece country band, we played weekends, mostly at American Legions, Animal clubs, VFWs, etc... None of us made enough money to cover expenses, but we had a lot of fun. There were times when I would pick up the M-Honer for certain songs, the mandolin for others, I tried the fiddle, but was not very good at it.
Along came the arranger keyboard, I tried one out at the local music store, fell in love and never looked back. The rest is history.

Now, after 30 plus years, songs still pop into my head and when I finish this breathing treatment and the dizziness wears off, I'll be at the keyboard trying a new rendition of The Nearness Of You. Yep, it's an old song, but I'm going to try a new spin on it. When I finish, I might post it here.
Good luck, from an old fogie,

Gary