Not saying the possibility doesn't exist on both fronts, but short of locking them both in a cage, there isn't much we can do to stop them, only make staying MUCH more attractive.
Changes that might make Jansson, Saiz, Alioski, Forshaw, Ayling, Dallas and a few others want to see us into the PL
Offload just about ALL the dross Orta (oops, vomited again!), foisted on us, in junior, development, U21/U23 teams
Sever the Cultural sh1thead deal
Sack Orta (sh1t, vomited again!)
Sack Bravo
Get rid of the majority of the coaching staff as they clearly couldn't coach if their lives depended on it.
Give Heckingbottom free rein to select and appoint a FULL coaching staff
Focus ALL the efforts of ALL those brought in to support the 1st team in developing a squad big enough to be competitive and resilient by seasons end
Invest over the close season in quality players to fill;
(and I'm going to be old school as far as positions go)
GK, RB, LB, CH, RH, LH, CF
Make Jansson captain until further notice, f00k this "few games at a time" nonsense
Between now and seasons end, if the club was make clear it's intentions on making 2018/19 the season Leeds EXPECT (not hope) to finish AT LEAST in the top 6, we might just encourage the good to stay, and the dross that they have no place at Leeds United.
If we don't do any of the above, and Heckingbottom is strung out as so many before him by a management who clearly don't have the best interests of Leeds United at heart, then although it pains me to say it, Marley is probably bang on.