Mandzukic is a rare breed of player. He is a fighter in every possible meaning of that word. He relishes a battle for first team positions while most other players start to be unhappy and wait for the position to open up for them. He has been in second or third attacking option at the beginning of every season in Juve and Bayern and somehow manage to battle his position to the top of pecking order while getting most of the supporters on his side as well.
He is not getting any younger so easier league and guaranteed starting spot would probably be safer option but I somehow doubt he will choose the easy way.
Compare the record of Mandzukic to Higuan for the past 4 seasons, you will understand that Mandzulic is just over rated and age is not on his side. He shouldn't be top striker for any competitive top club at his stage in his career.