So the the time lords were calling for the doctor through that crack and if he replied they'd show up and it would be bad. But then why did he hang around the planet? Were the daleks just going to raze the place anyway? Shoot the time lords through the crack or something?
Agreed with Phily B. This has happened before with Moffat finales, I find I need to rewatch and listen more carefully for very hasty bits of explanation to understand what was going on.