For example, has there been an event for a generation 4 game, while generation 5 has already been released? If no, does that mean events for generation 5 are no longer available due to generation 6?
Sorry, only events for current gens are released now. So, no more gen 5 releases, sorry.
There have been events where they give event Pokemon for the whole generation of games, not just the game specifically. However, not previous generations.
So, there will be no more events for Gen V games as Gen VI is out.
Hope I helped. :)
No, the last Gen 4 event Pokemon was a Shiny Suicune that ended on February 6, a month before Black and White's release in North America.
Game Freak will most likely focus on the new games, X and Y, and other future Gen 6 games (if any) rather than the Gen 5 games.