my wife has a work android phone and a personal iPhone.
as apple allows, I have her as a contact, with both phones listed separately. this isnt voodoo. its pretty normal.
when she phones me, it lists which phone its coming from. if I miss a call, I can return the call to the phone she used.
when she texts me though, it comes through to the same thread no matter what phone. that I dont mind, its neater.
but, the default is to text to her iPhone. so if her iPhone is dead, and she texts me from her android phone, and I hit reply, it goes to her dead iPhone. which is really stupid. just imho.
ideally it would keep the same thread but text back to the last text I received or in an ideal world it would be able to ping to see if the default phone is connected.