The oxygen should be fine. Even with no water flow, your aquarium should be populated so that your fish will have enough oxygen through surface exchange for quite a while. And you can always get a battery operated pump made for this purpose. The problem is temperature. It depends on your fish, Discus wil obviously do very badly with a large temperature drop. Mollies will be fine. A 125 gallon tank gioves you a huge advantage in that the water parimeters will change more slowly than with a smaller tank. You can wrap the aquarium in a blanket and this will insulate and prevent some heat loss.