Even though it's a complete speculation, but I think Dallas's best bet would be to try and tank diffing as much as possible now that they don't have Xzi. Other than a few map, since the meta has mostly been rush, they might try to field Sp9rk1e as their Zarya, a hero that he has historically excelled in while there are rumors of putting Fielder as their hitscan (assuming the new recruit(s) are unable to make it before the 1st week).

Considering how important Mcree is as a stable damage source and a shield breaker (with fan the hammer), I really don't see Dallas putting either of their flex DPS players to play him (remember Doha Ashe?) and actually might put Fielder to play him as Sp9rk1e plays the carry Zarya and Doha plays Mei.

P.S. One thing that led to this speculation is seeing Sp9rk1e play Zarya on ranked recently

P.P.S. I know this is a wild speculation but I'm just a worried DF fan that just wants to see this team do well this year and this team without a HS needs to get as creative as they can otherwise it's going to be a 0-4 start. Also, they can always try and play Mei/Doom rush but I think a well coordinated backline alongside a good Mcree would be able to counter that comp very well.