Today, January 20th 2014 AD of the Gregorian Calendar, is the wake-up day of Rosetta. Expected AOS window commenced at 1830 UTC before which Rosetta was expected to wake-up, and perform basic house-keeping activities.
AOS itself happened over 45min into the window.
If Rosetta had failed to wake-up of her own accord, was there a provision to awaken her by signal from Earth?
Rosetta was spin-stabilized during her hibernation, which means that the solar panels were not optimally aligned to produce all required power for its transceiver, so in a nutshell - no. Part of this is explained in ESA's Rosetta Hibernation Wake Up FAQ (PDF):
Q. How will ESA re-establish contact on 20 January? Will mission control send a signal?
No, just the opposite. Mission control will 'listen' for a signal that will be transmitted by Rosetta. This will be triggered by an 'alarm clock' timer that has been running throughout hibernation. The alarm clock will kick off an on-board wake-up procedure that will culminate with sending the first signal to Earth.
So since Rosetta would have to have her antenna pointed towards the Earth and sufficient power to listen in to any incoming signals, she had to do this wake-up procedure on her own. This includes her thrusters firing, star tracker functioning, antenna correctly aligning with the Earth,... for all of it to work. The contingency in case she couldn't complete these procedures was to simply repeat them until successful.
