Well, you're close. You've got the concept anyway.
Legally, for a 121 flight, a departure alternate must be listed on the release (it is not on the filed flight plan) if, at the time of your departure, the weather is such that a return to landing is impossible due to weather being below minimums. For example, lets say you are departing 18C at CVG with an RVR of 800-800-800. The approaches into CVG are all down to 1800 or 2400 RVR (CAT-II minimums cannot be used in this case, I think). Therefore you must have a departure alternate listed. The alternate must be within 1 hour flight time with 1 engine inoperative.
The return to landing is briefed in every departure. Weather/field conditions/local concerns are brought into this decision. It also depends on the type of emergency. In a quick return (smoke/fire in the cabin, aircraft uncontrollable) it will usually just be a lap traffic pattern. In a standard emergency (engine failure) there is a lot of time needed for checklist preparations.
Let me use an example that we frequently briefed:
Departing out of LGA, our departure brief would always include a return to JFK, never to LGA, due to the terrain around LGA (water) and short runways, compared to the longer runways, better more options for passengers, and our maintenance base there.
Another example (to use the checklist time issue):
Departing out of DAY or LEX, the brief would include a quick return to DAY, or else a diversion to CVG, since that is where we are based, we know the land, better maintenance, better passenger handling options, and it is only a 15 minute flight