Is there anything the Loyalists could have done after the Trident to win the war or was it over?

Maybe, maybe, maybe…if Mace’s army had teleported from Storm’s End to the capitol, he (or more accurately Randyll Tarly) could have won some last-minute victory. But even that would be rather risky, as the Reach’s numerical advantage would not have persisted if the Northern Alliance had been able to link up with Tywin’s army.