There are plenty of quality people that are sticking around. The people that I have seen leave on their own accord have been a mixture of high performers, clock watchers, and everything in between.
It's not all gloom and doom across MPC, especially at the legacy Andeavor locations. In fact, legacy Andeavor locations are still great and have for the most part stayed in fantastic shape despite the semi-purging of leadership. I am not a fan of big offices so I don't really like Findlay or San Antonio much but all the other regional offices have been terrific.
There is nothing I hear from my friends and former collogues at Phillips 66, Chevron, or Valero that would make me think the grass is any greener at another company in this industry. Friends in other industry do "cooler" stuff but don't get paid any better when I take in to account all of my benefits and compensation perks.