I was always holding out hope of a proper square digital sensor to keep 6x6 alive and kicking, but the biggest anyone's got is 53.9x40.4 in the latest $50,000+ ranges. With phasemiya only ever making 645 and hassy starting the 645 H-range a few years ago, 6x6 was always going to die this death unfortunately. They're still making adapters to put the latest digiback on V, RB/RZ, Hy6 and all those other defunct cameras, as long as they continue that, and 120 is around for us film-shooters, all of those systems will still be viable even if it just means we have to buy 2nd hand.
Still, think about how many people around are shooting on gear 50+ years old? I know that well more than half my kit is pre-1980, the V system is so ubiquitos that it'll be hanging around long enough for most of us to be old and grey.
But hey, think about this: when (the new) Hassy brought out the H1 and H2, they could take any digiback from anyone, as well as film. Not sure about H3D, but the H3DII locked out film, then the H4 locked out other brands of digiback. Only last year they realised their mistakes, and brought out the H4X, which can again take other brand digibacks, plus film again. They're obviously not above admitting their mistakes and bringing out a new product to compensate. Maybe if/when they realise that discontinuing the V system was a mistake, they might do a special run of V-cameras in 5 or 10 years' time?