Yes, definitely avoid the R talk. Until she's ended it with OM there is no R.
I think it's positive she expresses missing you. If she contacts you just be a great listener, ask lots of impersonal and upbeat questions (like you would a stranger you met), don't talk about yourself (your life needs to be somewhat a mystery), don't try to "fix" her problems, and make sure she can't help but leave the conversation thinking what a great guy you are to talk to. If she says anything that upsets you just say, that you have something you you need to do and must get going.
Also, the reason for not calling her back... You are just so busy! And life is good!!!
I'm glad to hear you have your parent's home as an option. It's nice to have emergency plans just in case.
Is there any chance you might be able to keep the kids in the same school if you have to move? I know sometimes one can get an interdistrict transfer. Is your W at least living in the district? Maybe you can use her address... Just some ideas to consider...
There is no arriving, ever. It is all a continual becoming.