Well, I am assuming your friend knows much more than me about microbiology, but I would have to disagree. I do believe the lacto and pedio will chomp on the sugars in teh wood, buch like brett, but I highly doubt there is enough sugar for them to sour the beer to a point where it would be over the top. I would have no reservations leaving the sour beer in the barrel for up to (and perhaps beyond) 3 years. At 8-9 months old, your beer is barely half the age it should be. Let it ride my friend.
As for cleaning it, you can. I wouldn't. Do yourself a favor and read up on the solera process. Mike T has a good write up on his blog.