I would say:
"While I don't believe in any deities in the sky, I do sincerely hope that the Doctors and Nurses who attend Chris are fully focused on their work and have the greatest skill to help this situation resolve successfully".

Maybe I missed it but I don’t see where they asked for a response. I don’t respond.

When most people are faced with their mortality the have a need to rationalize there is a higher power that can help solve all problems. Been through this personally and just tell a white lie that I'm praying for the sick person. Already a lot of emotions running high, I don't see how starting a religious arguement is a smart thing considering the circumstances

I'd probably just respond with "good luck". He's already doing the sensible thing. He went to the doctor instead of a minister which shows he doesn't believe prayer will fix what is wrong with him.

I “ wish “ and “ hope”...

I say I'm sending you good energy and you will be in my thoughts

The great sky monster demands a sacrifice!

Respond the same way you would if she had left the 'pray' sentence out.

I would say I will be holding you close in my heart.

If she knows you don't believe then she is probably not thinking straight. If she doesn’t then it’s not really the right time to tell her, just let her think you have.

Kind of a dick-ish moved to point out at this point, when she is so frightened for her husband, that you don’t pray, so “keeping you both in my thoughts” is both kind and honest.

I would either not respond or say that I will keep them in my thoughts.

Something like sending him you best wishes

Simply.. my thoughts are with you.

if its really going to hurt then I would just lie

Just say your thoughts are with you.

I usually say, "There is a power for good in and around all things, including your husband. This power is acting right now to create the perfect outcome."

None of my loved ones will ever think to include me in a such text , they know better . ?

shes worried about her husband and must not know about your standing on prayers etc i would just send a thoughts are with you hope all goes well txt then at some later point when emotions are not running high let her know you don't feel able to do so or not if you are planning on not having that discussion.Now is not the time to appear to be a dick her emotions will make it way bigger than it needs to be good luck

Say that you will pray for lord Baphomet as they asked. They will never ask again.
If they say that you should pray to god, you choose any famous pagan god and say that you will pray to it.
If they insist about the real god you say that there are no real gods, and they should be more specific about which imaginary friend you should pretend to have a telepactic conversation.
If they say lord Jesus or the christian god, at this point you might just laugh that they are trying so hard.

If it's an immediate family member then I would text, "I hope he gets well." If it is a distant family member or non-family, then I will ignore it for not showing me respect for my beliefs.

That’s not my ball of wax, but I wish you the best possible outcome.

Cross my fingers?

I give them medical advice.

I experience that all the time. People often ask you to pray for a whole lot of different things. I just interpret the situation as them wanting to hear words of solace and assurance. I usually say something along the lines of: "Sure! I'm sure everything will be fine and if there's anything I can do, I'm here for you". I think it's best if you make sense of this message in terms of the bigger picture and not take it at face value.