When Sony acquired Bungie announced that all future Destiny 2 expansions and all future Bungie games were going to continue releasing everywhere day one and full featured.
Marathon was announced as such, with Xbox and PC versions day one.
Any day Hermen could change his mind, but considering Sony is expanding to more platforms (Sony mentioned when acquired them that the Bungie acquisition was part of it, and now even announced Lego Horizon for Switch) I highly doubt they'd drop the Xbox version and even less the PC one.
If Xbox continues decreasing its market share to a point that most 3rd parties stop supporting it and MS stops making their own Xbox hardware and replace them with PC shaped consoles running Windows then Sony obviously would stop releasing Xbox versions. But since these new "Xboxes" would be running PC (including Steam) or a potential future Sony PC store then Sony would continue supporting them.