If you want your hair to be blue again on top of your highlights then the best thing to do is to let the hair fade until it is a very pale colour. Now as it has had a maroon colour applied to it, it may never fade to white so the best you can hope for is a pale pinkish tone. Then afterwards if you want a blue that will last choose a deeper shade than you want as it should last that little bit longer.
Blue is such a delicate tone that it never lasts long in the hair and you have to expect a certain amount of upkeep to maintaining a nice shade. I have a client who re-colours her blue hair every week to keep it looking true blue.
Remember that bleached hair is porous so use a shampoo and conditioner that is designed for coloured hair to help prevent your colour from fading.
Hope this helps!