Rough one if the creator's actually gone dark, that project's been load-bearing infrastructure for a long time. A few things holding the fort while the dust settles:

• The AUR package might just be pulled because the upstream download link broke, not necessarily dead-dead. Worth checking the AUR comments or grabbing an archived copy of the last known-good installer if you need to keep ripping today.
• makemkv-oss exists as a stripped decrypt-only fork on some distros, handles the AACS/BD+ decryption piece even without the GUI wrapped around it.
• For the actual muxing after decryption, ffmpeg with libbluray compiled in will read a decrypted BD structure fine, it's just not as one-click as MakeMKV was.
• The part that's genuinely hard to replace is ongoing AACS key updates for new discs, that's usually the real value MakeMKV was providing beyond the rip itself, not just the tool.

Hoping someone picks it back up.