This is up to you. You can still get some rewards, but events do not give you any other major rewards if you have completed all achievements/tasks.

Mission events - if you continue sending girls out on missions, you have a chance of getting boosters, time skips and permanent multipliers.
Clicking events - if you continue using tickets to click, you have a small chance of getting keys, time skips, or boosters.
Card events - if you continue using tickets to click, you will get one of the following event items: keys, time skips, boosters, or permanent multipliers.