Flight plan departure procedures vs real life departure procedures In the flight plans there are included departure procedures. However, sometimes something can change eg. different runway is assigned by ATC and then departure procedures in the flight plan is invalid, because SIDs are assigned to the runways. 


Are flight plan amendments send after such change?
Does it happen often?
How airline dispatcher knows which departure procedure to fill in the flight plan if he doesn't know which runway will be used in the future or what will be the wind direction etc.
1) Not to my knowledge, these are short-term deviations from plan that do not require an updated plan (similar to ATC offering direct routings - shortcuts).

2) Not sure. What qualifies as “often”?

3) Experience, local and airport procedure knowledge and a weather (wind!) forecast go great lengths in predicting departure runways and routings.