Yeah, but how interesting would that be? 
Besides, it makes sense that a hot fusion reactor would detonate rather violently if the containment thingy is breached. The release of untold billions of joules of energy = ouch.
No, it doesn't make sense. You can go over to the Classic Battletech forums and post a thread about this if you want a lengthy explanation. CBT establishes that the only way a 'Mech is rendered totally unsalvageable (i.e. engine destroyed, presumably by cataclysmic detonation) is if its center torso internals are totally destroyed by an area saturation artillery attack.
CBT fusion engines are extremely safe. Mike Miller, materials engineer on the CBT writing staff, can give you a better explanation as to why.
Cooking off ammo will blow off limbs. Exploding reactor, which then cooks of all ammo, in addtion to the enormous energy realeased from a failing fusion reactor.
Again, failing fusion reactors don't release enormous amounts of energy. Google-Fu provides some basic evidence. Nor have exploding reactors ever done
any damage in the Battletech universe.
The reason is that the fusion reaction ends very rapidly once containment is breached. What little plasma escapes will cool off very fast. Fusion reactors are, unfortunately, rather safe.