roljoe,
With due respect, I think the OP was most likely not referring to the most extreme case. As you say, obviously if you suffer an engine failure or sustain obvious damage on takeoff, you'll most likely not continue to destination, but neither will you necessarily return to the departure airfield or use the same runway at that airfield. There are many things to consider.
The question (in my opinion) is asking what to do if you suspect, or even have it confirmed that you hit birds on departure, but have no abnormal indications or handling characteristics as a result. Basically, there are no hard and fast rules. There are a number of factors to consider, but ultimately the crew have to make a decision based on what information they have. It's also perfectly possible to suffer a bird strike without even knowing it, and discover it on the next sectors walk around.