It is a shame when any of the attractions have to close, especially one as popular as BTM, but there'll be so many other things to do and you have Buzz to look forward to, from the reviews I think it'll be a big hit with your DS.
I notice that you're planning another trip next year so BTM'll be something to look forward to then.
I have to admit to always checking beforehand what attractions are due for rehab. I don't think we could bear a trip without going on POTC, closely followed by BTM.