sounds bad. BTA are some of the most durable anemones in the hobby though. If you provide it with a proper home and feed it properly it can recover from expulsion of its zoox. The gaping mouth however; is very troubling. Unless there is some obvious stress (short acclimation, high ph swing, unstable temp, ammonia or heavy phosphates in the water) that can be corrected or mitigated then the only thing you can do is wait and watch. As soon as his mouth starts closing try and feed it finely chopped silverside, squid, scallop or shrimp. If it doesn't close up in a few days I'd still try and feed it and see if it CAN close its mouth enough to digest some food.