Dire-Strain Rampage

You can cast a spell using flashback even if it was somehow put into your graveyard without having been cast.

A spell cast using flashback will always be exiled afterward, whether it resolves, is countered, or leaves the stack in some other way.

If the target permanent became an illegal target by the time Dire-Strain Rampage tried to resolve, the spell won't resolve and none of its effects will happen. No player will search their library for any cards. However, if the target is still legal but wasn't destroyed, perhaps because it was indestructible, its controller may still search their library for a basic land card (even if the target was a land).