The Red Bull has not been declared illegal. The FIA Technical department has said that in its opinion the floor does not meet the rules as it interprets them. If red Bull wishes to go on using the floor they can. They would then be reported to the FIA Stewards, who would rule on whether the opinion of the FIA Technical department was correct or not. If Red Bull did not agree with that, it could appeal to the FIA International Court of Appeal.
However, Red Bull will probably decided that it is best not to go down this path. This is an alternative way of solving problems to having protests and it is much more sensible than having the result of events left hanging in the air.