Contain, wait for HRT or CAG. This type of scenario is beyond the capabilities of most SWAT Teams, and most hostage incidents usually only have one hostage taker. We typically train for scenarios with multiple suspects, but not 30. I think everyone is a little too hard on the Russians about these incidents, because they are handling truly extraordinary hostgae situation with no real paralells. The theater incident last year was actually pretty well handled, even with the massive loss of hostages, because just about any other plan would have led to the deaths of ALL of the hostages and all of the rescuers. Their major screw-up on that one was not having an adequate follow-up plan for providing immediate medical evacuation and care for that many hostages, and is what led to the unfortuante deaths, but they are lucky that they did not lose them all.
This school incident sounds like the terrorists had a negligent discharge of their explosives, which triggered an exigent hostage rescue attempt, which came off quickly, and did its job, though there seemed to have been massive amounts of confusion. If faced with similar circumstances, I don't know that I would have a decent answer, either.