I am not sure I would call it fear, but players definitely don't want to get cut or benched. Nobody has a 100% guaranteed contract so if you get cut that means you might lose millions. Let's look at Zeke's contract: $90 million total, with $50 million "guaranteed", but the reality is that only $28 million is 100% guaranteed. Per another site "If Elliott is on the Cowboys roster on the 5th day of the 2020 league year, his 2021 salary becomes guaranteed. If Elliott is on the roster on the 5th day of the 2021 league year, his 2022 salary will be fully guaranteed."
Said another way, if Zeke sucks in 2020 and we cut him, he will miss out on $45 million out of his $90 million contract. I would say that is a strong motivator to perform. I know $45 million is enough to last a lifetime, and most of us would be ok with "just" $45 million, but for a rich person, $90 million will always be better than $45 million.
My point is that coaches can definitely enforce discipline as long as players believe the coach is really in charge and has the power to cut them. Right now, players can see that MM can fire and hire coaches as he pleases, compare that to JG being told he had to promote Kellen and let him call plays. We will see if MM is given true power, but so far it looks good.