If the club can't sell Suarez that has nothing to do with Koeman, if he stays then he should use him, there is no point paying the guy 25m a year and not play him occasionaly. Koeman doesn't want him here thats for sure but it is up to the board to get rid of him, its not Koemans fault the club gave players who are 30+ long lucrative contracts.
There is even less of a point to play him regularly because
1. he is shit
2. he makes the team shit as he fucks up lots of attacks
3. if he plays regularly it means he will pass the 60% game mark, which will activate the clause that will extend his contract by a further year, which means we will have him for another year with high wages.