Mom has bought you and your little brother two small cakes. She puts them on the table in front of you two. Suddenly, your phone rings; you go out to your room, and when you come back both cakes are gone. You say:
The little creature didn't ask me for it; he was just waiting until after I . . . . so he could gulp it down in one piece.
My question is: what verb form fits better in the blank?
I've heard left (simple past) used in a similar situation, but is it the best choice? Other possible answers would be was gone, would leave, had left, etc.
Just an attempt:
I guess one way to solve the problem is bring everything to the present, find the answer, and then backshift them all to the past.
He is waiting until after I . . . . so he can eat my cake.
I think leave and am gone work well, and so does have left (to a lesser extent, because I prefer to use the simplest form possible in the subordinate clause). Will leave sounds just wrong.
Following the scheme, the simple past (left, was gone, etc) will do fine in the original sentence, and had left/gone is a possibility, but not would leave.
But I'm not sure about all this.