There can never be SCIENTIFIC evidence, probably - but if you have seen a soul with your own two eyes, or communicated with a soul, that may be evidence enough for you.

A bit of an analogy - where I live, the "scientific" claim was long that there are no cougars hereabouts (a claim since modified or rescinded, I believe) - however, for just as long, there have been people who have claimed to have seen cougars on backroads, at the edge of their woodlots, etc. Now, if I were one of those people, I would certainly believe that cougars are around here, whatever scientific inquiry finds. Heck, if I laid eyes on a sasquatch, that would be evidence enough of their existence for me.