If these sprites have bullet behavior, you can add an event like this:
Sprite->Compare X -> greater than 2000 -> Sprite Destroy
2000 here is just an example. If your layout is not scrolling, this can be a fixed number greater than layout width plus sprite width. You don't have to be very precise, just put a number that's definitely outside of the layout.
If your layout is scrolling, you should use something like "greater than (scrollx+WindowWidth+sprite.width)" or something like that.
Another easy way to ensure that sprites get destroyed is to add Fade behavior.
Set Fade in=0, Wait=20, Fade out=1, Destroy after fade out=yes, and your sprites will be automatically destroyed after 21 seconds.