There was a study done by a Boston University professor on true percula social rank. He wrote that in a group of clownfish theres a strict order of a dominant breeding pair. Subordinate clowns stay in their lane because they wait for their opportunity/time to become a breeding male or female. All of the new settlers in anemones are recently hatched clowns (non-threat) that are accepted by an established breeding pair.
Now to your question. The same study showed that clowns never "migrate" from anemone to anemone for two main reason. Invading other anemones and clown groups doesn't always mean they can take over the dominant pair there. The second main reason is clowns can easily fall prey to predators due to their poor swimming skills. So based on that analysis I'd say that the majority of clowns wouldn't be able to survive without anemones in the wild.