what would you do if your greatest talent became inadequate?

It depends on HOW it lost all meaning. If there is another meaning to be found, more stable one, or another use of it with same or different meaning. Depending what meaning is good for you and most stable, most rewarding in its meaning.

If you can't do the very same thing, then damn, start everything else you'd like to be doing, you'd enjoy being done or being done. Eventually you may want to narrow it down, shift between a few things in time periods. Never fear to start new and to learn new things, because you're ever as old as you make yourself be. You are as unfit as you make yourself be. Because there is always something you can do well, be it building rockets or telling stories. Find what you like and improve, always.

If I didn't answer well enough you could ask anything more precisely? :)

I would try to work toward my plan b. I'd be foolish not having a plan b.

be bitter then accept