There is no need for that if statement. Rosetta's antenna needs to be very precisely oriented to maintain connection, and it is attached directly to the side of the spacecraft (as in, it cannot be aimed without moving the entire spacecraft). The moment Rosetta hits anything, the antenna will be knocked out of alignment, and if a corner of it is resting on the comet, it cannot orient itself properly to establish a link.

Yes, but there's a fairly high risk the computer or its power supply will malfunction on impact.