What does your T think about you reaching out to him? I know she wanted you to wait for her baby to be born and her maternity leave to end to send the letter but does she think you going back is a good idea?
Why I'm asking, you seem to be doing great last few weeks and it all started after you terminated your other T and then this PDoc terminated you. I do have to wonder if him taking you back would be such a great thing for you. All transference and attachment aside- was he a "good enough" PDoc for you?
Could be my thing though I hate ultimata and his "rules" were a bit too much for me. Just don't forget who's working for whom.

Also there's the possibility of him refusing- I do hope you've talked with your T about that and know what it would mean to you. Not saying he would...