I would not worry too much about the Hy6's future path. First of all, Sinar has indicated that it will continue support and is looking into future development. Second, after the demise of F&H the activities in Braunschweig have been continuing through DHW (details not yet fully known, but in any case with a smaller group of people). Third, while Leaf is no longer in the AFi business after the takeover by PhaseOne, the latter is examining the possibility of continuing this line of business. So, the overall picture -while not cristal clear yet- is not so bleak.
For what it is worth, I bought a new Rolleiflex Hy6 from F&H like a month ago. For the moment with film backs (regrettably only 4560 type but F&H is aware that there is quite some demand for a classic 6060 back). I am looking into the possibility of adding a digital back but that is not my priority right now since I use a Rollei DB20p (PhaseOne 20p) with my Rolleiflex 6008 AF.
The most elegant solution seems to be the Sinar eSprit 65. But also other Sinar backs will work fine (e.g. eMotion 75).
The most advanced Hy6/back combo would be the Leaf AFi-II 10 (very wide angle), but it is no longer officially offered by Leaf pending reassessment of the situation. Adding a stock Leaf Aptus back to the Hy6 may not work from what I see on the Leaf web pages. So, if you want a Leaf back, get one of the AFi combos (and you will save as well given that the camera body is almost offered for free in the combo price).
For some further information, see my web pages.
Pascal