From what I have read, Mantle was convinced he would die young. All the men in his family did - father, uncles, grandfather. Of course they were miners not ballplayers. Nevertheless he lived it up burning the candle at both ends. Reportedly he was very shaken up by Roger Maris' death when Maris was only in his early fifties, as Maris was a comparatively clean-living family man. Didn't stop Mickey from partying though.
The best story I heard about the contrast with Maris' character was a story told by a teammate. He was building himself a house during the offseason, so Roger packed a lunch every day and showed up, unpaid, to help.