I didn't find any specifics on death rates in my search through the legalese, but I remember reading a comment sometime before Reddit killed third-party apps from somebody who works in a lab with nematodes that animals more complicated than those are regulated strictly enough that even a single death under your watch can be grounds for termination of your license when you get up to monkeys and such.

[–] [email protected] -1 points 11 months ago

From your own sources:

Neuralink treats animals quite well compared with other research facilities, employees said in interviews, echoing public statements by Musk and other executives. Company leaders have boasted internally of building a “Monkey Disneyland” in the company’s Austin, Texas, facility where lab animals can roam, a former employee said. In the company’s early years, Musk told employees he wanted the monkeys at his San Francisco Bay Area operation to live in a “monkey Taj Mahal”, said a former employee who heard the comment. Another former employee recalled Musk saying he disliked using animals for research but wanted to make sure they were “the happiest animals” while alive.