Well...the BMG is a permanent show so yes...it will be performing next year. I haven't seen the show personally but everyone I've asked said it was great!
Yes, its permanent. Yes its a must see. No its not included, you have to pay seperate, its about an hour and 45 minutes long. No they do not talk, its funny, music intensive with toilet paper, loud noises, strobe effects, and twinkies.
It is absolutely a must see. We weren't sure if our 5-year old would enjoy it (we nearly left him at the Portofino Kids Club), but despite it getting dark ever so briefly a couple of times, and loud, he proclaims the show as his favorite part of the trip.
One thing to keep in mind is that we booked at the concierge lounge at Portofino and got kind of crummy seats (well, none of them are really bad in a 1000 seat theater), but when I was at the ticket counter for the theater, they upgraded us to 7th row seats, center section, which was wonderful. It sounded like another small group had similar fortune, so you might want to check the theater booth soon after it opens to see if they have released better seats.