Mom, stroke 2016 is home and dad is in a facility. She wants him home before they die, what to say?

You don't honestly give us enough information. Who lives with your Mom. Does she have 24/7 caregivers? How much care does your Father need. Just offhand it sounds to me that this would not work. Romantically it sounds lovely, but no one is dying here at the moment, and this could go on quite a long time, and surely there is a "reason" or two that Dad was placed in a facility.
Without more information I would suggest, if there is a financial way to do this, that Mom joins Dad in his facility. Is it memory care? Board and Care? Assisted Living care?
I am assuming Mom doesn't live with YOU. If you are asking if you should be taking on the care of both of them I would always vote no. This is killing work, to be frank.
Give us more info if you are able, and wishing you best of luck in this decision. This may come down to "Mom, we are so sorry, but this just cannot be done." No argument. Just "I'm so sorry; we can't fix everything".

Can you fill in some blanks please?

You don't say how "bad" dad is, but who is going to be taking care of him? It does not sound like mom is in any shape to be a caretaker of anyone.

Sure - sounds very romantic - but definitely not realistic!

If it's not a safe option, just give a vague answer and change the subject.

Not enough information, however can't mom and dad be together in a home? If not then just say ok, I understand ,to her and move on.

Take mom to facility instead. Do NOT take him home!!! Only do this if you want to die before them.
Hugs 🤗