Yes, as announced by DSA, the powerpc buildds have been shut down:https://lists.debian.org/debian-powerpc/2018/06/msg00004.html
Tears in all directions. At least from those of us that love our risc architectures.
We are currently in the process to properly move powerpc to Debian Ports. In the meantime, you can either reinstall your machine with Debian ppc64 from Debian Ports [1] or wait until the transition is finished. Jessie on powerpc is no longer being updated and supported. You will have to switch to Debian unstable.
It is perfectly possible to install the last supported 64-bit release and then dist-upgrade to sid and everything seems to run just fine. I am having no troubles ( nothing fascinating other than some datatype weirdness ) on a PowerMac G5 :
nix$ uname -a Linux nix 4.17.2-genunix #1 SMP Fri Jun 22 23:42:51 GMT 2018 ppc64 GNU/Linux nix$ However I really should yank the disks out and try the latest installer with grub2. Just for testing. Dennis ps: the next big *thing* will be RISC-V which I am also interested in