Firstly, <font color="red"> </font> HAPPY BIRTHDAY TO YOU!!!!

Second, I love your question! Seems like a transference thing to me and if it was me I'd def. ask it. I'd hope my t would not respond in the here and now, I'd hope she wouldn't tell me how SHE would feel if I left. I'd hope she'd inquire and elicit from me about my wish, what I would WANT her to feel about a separation, and perhaps talk about how I would've wanted mum to feel about our separation...and perhaps mourn the lack of it....

And I do understand your desire to hear from her, in the here and now, as your t and not as your mum.....perfectly understandable....