AirAsia probably have some company much nearer than SEN to do their maintenance for them. The fuel cost alone would be astronomical, so I can't realistically see them sending a plane to the other side of the globe for it. The only time you'll ever see an AirAsia plane at SEN is if it was being shipped to a new owner and was forced to make a pit stop there.
On a side note (albeit a bit late), having flown on AirAsia A320s twice in the last year the recent event is very sad news indeed.