Would plasma skin tightening fibroblast be a good option for marionette lines? (Photo)

No, I do not think PRP by itself will get you the result you are looking for. Your issue is volume loss and so a filler is the treatment you should be looking at. If hyaluronic acid based fillers like Restylane are not lasting, then you could consider a collagen stimulating filler like Sculptra Aesthetic. This is a deep fold and full correction may not be possible. 

You are in a tough situation having tried multiple treatments from what sounds like reliable providers. There is another option to consider that may make sense to you.  I agree that platelet rich plasma (PRP) alone will not likely be successful. However after looking at your photo I have seen patients in your situation respond very well to a combination therapy. There is a powerful technique utilizing the mix of PRP with either a hyaluronic acid filler like Juvederm or a collagen stimulating filler such as Bellafill along with PRP. This mix is injected directly in the area of concern along with injection in structured/scaffolding areas that support a “pull up” on the marionette lines. The PRP/filler mix works very well together in maximizing a good result in difficult areas. Find an experienced provider who knows this technique. Let’s us know how it turned out for you!

If fillers didn't work I don't believe that skin tightening fibroblasts would benefit you. I'm not sure why filler doesn't seem to work for you. You have very deep lines and you would need more filler than the average patient. You may have been under-treated. With the life span of filler and the amount you would need it could get expensive to keep up. At this point you may want to consider a face lift. This will give you the results you desire, and be a longer lasting solution.