While there might not be legal consequences for Michael, he could run afoul of the Nevada Gaming Commission. The Commission was formed in 1958 to try to "clean up" Nevada's gaming image because it had been exposed as being run by the Mob. The Commission had a "Black Book"--a list of people who could be barred from even entering a casino, much less owning or operating one. They could be barred even if they didn't have a criminal record--just unsavory reputations and associations could get someone listed in the Black Book. Michael could have lost his casino holdings simply because his caporegime, Rocco, murdered someone.
That is why he used straw men to run the casinos for him. I also think that by that time Michael would have had enough "pull" (such a Nevada Senator Geary) to prevent him from being listed in the Black Book by the Gaming Commission. Also bear in mind that very rich business men such as Michael would be important for Nevada's (and in effect Las Vegas) economy.
