The number of years doesn't really matter. I seriously doubt that he's gonna last that long. If he has to be canned he will be. Some coaches have been fired after year 1 of a 5 years deal before so it's not uncommon.
That said he deserve to stay in post for now. He's coming off two 100pts seasons and one ECF after the team finished dead last in the east the year before he took the reigns of the team. Love him or not , agree or not , it's understandable why MB is keeping him for now