I know some folks that live happily on $10K a year and some that need 20x that amount. How long is a piece of string? It depends.
You also need to classify what "retirement" is. Personally, I don't think I could ever just pull the pin, pull up the lawn chair, and "retire" as in the way that many think of it. My father "retired" in 1987 and still works. I don't see a career/full-time/etc life, but don't see myself not doing something. (when not climbing/skiing)
We won't need the house, omg, way too much room and too much upkeep. Downsize. A nice ski-out condo at Red Mountain can be bought for ~$450K less than my house, so there's a nice move. Living costs there are lower than here, especially in property taxes, so that eases the operational budget. $8-10K a year on kid school/etc will be gone. Etc, etc.