I don't see the colors going away permanently. Maybe temporarily. If a new MkVIII were to ever come out, purple and pink could return without much issue by then. I suggested in another thread they can have a Monorail Aqua... a nice Blue-Green color stripe.
Also , here is an argument for keeping current colors and not change a thing. When the colors are changed, we will still know it was the physical monorail in the accident. The 11th one is likely to be the former Pink, the 12th likely the former Purple. So why kid ourselves, we know what it is no matter the color. Austin would probably want it left alone. With how much of a fan he was, I doubt he would push for the retirement of any color.
Its a shame that those two colors may disappear! The the two most princess related colors for the girls.