The Nazis actually had a policy of killing their slave doctors every 6 months. There was no, "until they stop being helpful". It was mandated to be 6 months. (but some camps were slightly more lax about it)

It was all pretty horrific, and the worst part is, the Nazis themselves never had very competent doctors, which is why they forced actually competent Jewish doctors to carry out the twisted experiments.

There are very few books written by people who survived the camps, and the one by Miklos Nyiszli is likely the best account of what these doctors were subject to.

Behind the Bastards covered this on their Mengele episode, which I highly recommend. Robert Evens had a more sympathetic outlook towards the jewish doctors who were useful to the nazis.

Basically, they were put in a terrible situation, and they were able to use their relative privilege to help other internees. And it isn't like they were living the life of luxury, they were all murdered on a regular basis so that they individually wouldn't become to important to the death machine. We shouldn't judge those people too harshly given the choices they were given essentially.

And, I am terrible afraid of the right wing in the US. They aren't even hiding their intent to do a genocide anymore. I live in a progressive enclave of a deeply red state. Needless to say, I'm armed and I encourage all my progressive friends to get armed.