Even though I stick with Carrara and rarely use Daz Studio, I am sad that Daz is phasing out the 3DLight rendering engine.
I rendered all my DS stuff with it in the past, and never really used Iray. Of course Iray is much better, but also soooooo slow. Will people use Iray from now? Filament?
In any case, if I got it right, there will be another, last DS4 release on december 29 that will include 3DLight. After that, you won't have it anymore...
Daz 3D
I'll definitely keep the backup of older copies of the app!
Another way to download it offline, is going to your Daz account >> product library and then filter for "Daz Studio 4.x". You should be able to backup the current copy of Daz Studio.