I see your point. However, integrating Rust properly in the Linux kernel is an uphill battle. Redox OS is not at all close to being stable, but it showcases that you can build a Rust kernel from scratch, and integrate it into an OS that meets some of the requirements of a modern one. Of course, considering it a toy project and glancing over its potential doesn't help with adoption. They even mention in their description that currently they can only support a community manager and a student developer with the current donations. When you compare that to the amount of money and developers involved in the Linux kernel, it's insignificant.
I was not suggesting that the Rust For Linux devs jump ship, but it could be beneficial for the investors behind the project to look at alternatives. Heck, the Linux kernel started as a toy project itself. I believe that a team focused solely on such a Rust-only kernel could spearhead needed changes to reach something stable, as opposed to investing time and money into fighting established C developers to integrate a memory-safe language in the kernel fully.
The go-to monkey paw scenario could work, where they receive immortality, but have to serve the summoned entity forever as deformed (and perhaps always hurting) "things"? However, that is maybe a bit too predictable. What if they mess up the spell and instead mark themselves for sacrifice?
They slowly realise this due to a symbol appearing on them, which could slowly spread further on their body (maybe hurting too). You could make it more interesting by pitting them against one another by suggesting that only a few have to die for the sacrifice to be complete. If their characters are not that close to one another, it could lead to some interesting decisions on their part, haha.
The process could span a week or more, where their body gets engulfed more and more by the mark. They could use this time to review what went wrong in the summoning process, and how to potentially reverse it. I'll leave those details to you, if you're interested in pursuing this idea :D