A pattern's fate is the result of evolving said pattern until its final behavior is known. This answers such questions such as whether or not the pattern remains finite, what its growth rate is, what period the final state may settle into, and what its final census is. All small Life patterns seem to eventually settle down into a mix of oscillators, simple spaceships, and occasionally small puffers.
Most sufficiently large random patterns are expected to grow forever due to the production of switch engines at their boundary. Engineered Life objects -- and therefore also sufficiently large and unlikely random patterns -- can have more interesting behaviour, such as breeders, sawtooths, and primers.
A pattern is said to have an unknown fate if its fate is in some way unanswerable with our current knowledge. The simplest way that the fate of a pattern can be unknown involves the question of whether or not it exhibits infinite growth. For example, the fate of the Fermat prime calculator is currently unknown, but its behaviour is otherwise predictable.
A different type of unknown fate is that of the Collatz 5N+1 simulator, which may become stable, or an oscillator, or have an indefinitely growing bounding box. Its behavior is otherwise predictable, and unlike the Fermat prime calculator the population is known to be bounded.