How can I get the most out of final sessions with my beloved therapist who's retiring?

TL;DR expressing my grief and fear about therapy ending, asking how I can get the most out of the last few sessions. 

I've been with my psychotherapist for 5 years, plus a 6 month stint about 10 years ago. She is retiring in March. Because I am physically sick I only see her every 3 weeks. That means we've only got very few sessions left. 

I've seen her more frequently than I've seen any friend - I saw her weekly for years. She's the only person in the world that knows all the dark things about me. She knows things I've never told anyone else. 

I am scared to be without her. I've started looking for a new therapist, and it's made me realise how flexible she was for me. When I became disabled and couldn't work, she let me pay less and reduce down from weekly sessions to three weekly. Not everyone has the capacity to accommodate me. 

I've been on this huge personal journey with her. Not even my best friend understands, and my best friend is awesome. My therapist has just been the best. So kind, supportive, non judgemental. Funny sometimes too. Unendingly interested in me. I know it's her job, but it's authentic. 

It's difficult for me on a practical level to find a therapist so I'm afraid that there will be quite a gap without one. I am afraid to be unsupported, even though my mental health is pretty good right now. Therapy has given a rhythm to my time. 

There will never be anyone like her to me. I don't think I could ever replace her. I'm sure I'd get a lot out of other therapists but it could never be the same. She's been my guiding light through my 20s. I've learnt so much from her. Being with her has just been how my life is. I am losing something good from my life. 

I can see I will have to grieve more tears than I anticipated. Therapy is a one sided professional relationship, I feel like I shouldn't feel this sad, but I really do. I'm not just losing support that I pay for, I'm losing someone that's helped me form my character, my best teacher. I hate feeling grief, I feel like I might explode with tears, they can't come out fast enough. 

I know she's going to go on and have a lot of adventures in her retirement. It will be good for her, and it will be good for me to see if another therapist can help me get past some hurdles I've been stuck at. 

I feel like I want to make the most of our last sessions, like it's the last day of a holiday. I want to soak up all the wisdom I can get out of her. I don't want to take up a lot of time crying about our parting. I want to figure out questions to ask her and issues to bring her that would help me feel a sense of completion of our time. Does anyone have any ideas about this? 

Has anyone ended therapy in a good way before? What did you do, what felt right? I'm not ready to leave therapy so there's no sense of my personal chapter ending, it's just our relationship that is. 

Did you ever meet your therapist socially after therapy ended? My therapist has said she'll tell me about herself once we're done, which I am looking forward to, but I don't know what our relationship would be like. 

How can I make this ending the most useful possible? How can I make it feel complete?