Best case, and I have a gut feeling the one that will happen: there is an eruption but the flank doesn't let loose so no tsunami.

That would be: devastation delayed for another day.

Worst case: flank lets loose and a very large tsunami hits as postulated.

Medium case: flank lets loose and due to unforseen factors (loss of energy in trenches, reverse currents, act of God) it is not as devastating as thought and maybe only a 20 foot wave hits and there is still staggering losses but not as bad as it could have been.

This time...I vote for best case. Next time, I hope for medium case!