I've done some research and found that the study of imaginary friends in adults and children is very limited.

Some things however are generally accepted:
*Having imaginary friends is a sign of intelligence. (ie: people with imaginary friends tend to do well on IQ tests [though not all people with intelligence have imaginaries]).
*Most people are happy living with their imaginary friends.
*Most children who have imaginary friends abandon them into adulthood.
*Some adults carry their imaginary friends into adulthood others pick them up in adulthood.
*Adults with imaginary friends report that their imaginaires do not hinder their life or their relationships with real people.

More study would be needed to find if these points were consistent across a wider section of the population... but there you go.

I would also personally argue that having imagination and fantasy is not totally different to having a 'person' that is not real to talk to. The latter is simply a more advanced and complex form of the former.

I would also think that having a prolific imagination, which is advanced brain functionality, is very different to schizophrenia, which is a result of faulty brain functionality.

Blessings
Cat.