An object whose fate is unknown, except that it appears to grow forever in an unpredictable manner, is said to exhibit chaotic growth. In Life, the only chaotic growth patterns known as of January 2019 are meta-patterns in explosive rules simulated by the 0E0P metacell (none of which have been explicitly constructed). This is in contrast to many other Life-like rules, where even small objects can appear to grow chaotically.
It is possible that chaotic growth may occur rarely or even regularly for large enough random Life objects, but if so the minimum size of such patterns must be larger than what can currently be experimentally simulated (but see novelty generator).
In any case, it is not decidable whether a pattern that apparently grows randomly forever is in fact displaying chaotic growth. Continuing to evolve such a pattern might at any time result in it suddenly cleaning itself up and becoming predictable.