First, I'm fairly sure both the Beeb and the Mouse Corp are watching Doctor Who ratings on a much wider timescale than the armchair analysts, worrywarts and doomsayers out there.
I don't know how long Disney secured distribution rights for but with their penchant for hoarding IPs they might even be in for a long game of securing international rights for the entire series back catalogue when they expire with other parties. Star Wars, the MCU — they know from experience what kind of synergy a 60 year franchise can build when it's collected in one place.
Second, though, we'll have to see if Disney'll invest in the spinoffs right away. I'd love to see that "War between the land and the sea" thing materialise, whatever it is, and it sounds like Bad Wolf have been setting it up. As for the UNIT show, if that's even separate from the other spinoff... at least the primary set is already built?