im having more thoughts about that tmnt sweet toot au. i think Splinter (still Hamato Yoshi) and his wife were on an ill-timed trip to New York when the sick broke out, and they ended up sort of stranded because in an effort to contain the sick, no one was allowed in or out of the country. Tang Shen unfortunately caught it, and after her death, Splinter kinda just gave up on life and went to live in a cabin in the woods while quietly hoping the sick would claim him too. hes been out there alone for a while when he finds the turtles and they restore his will to live :)