G.L.
It is possible that you don't get it out. But one thing to try that might work is hand sanitizing gel. Rub it into the cloth, rinse, repeat, and repeat until as much of the marker as is going to come out is out. Be aware, though, that the hand sanitizer may also remove color and designs from the cloth.
If it doesn't come out, another option is to redecorate the t-shirt. Get a pack of colored sharpies, stretch the t-shirt over a piece of cardboard, and draw something fun over the marks. My mom refers to things like this as "opportunities to get creative."
Good luck.