It is technially lost forever this is why I dislike unreal converting all stuff to its binary .usasset files.
You can of course open the image up and print screen it at full resolution and then stitch it back together but you’ll lose any alpha channel.
I dont know of any way to convet from .t3d to image formats. .T3D is a text format that has information about that asset for moving assets between projects. Same with .copy I beleive.
You are right clicking → export right?
Hope this helps
Don’t forget to accept an answer that best clears your question up or answers it so when the community finds your question in the future via search/google they know exactly what you did to fix it/get it going.