I don't think this idea would really contribute to the overall enjoyment of the game. Pretty much the opposite: It could create very rare, but very frustrating win-more or instant loss situations over which nobody in the game would have any control at all.
Just imagine the assault lance hanging back together (as is often the case), and a few lights ambushing them. They manage to take out one of the assaults, he'd randomly blow up and heavily damage or even destroy his bystanding friendlies. In that case, the light mechs would have just destroyed the entire assault lance, just by rolling the dice and hitting this very low chance.
This may make for a fun highlight reel for the light mechs witnessing the fireworks, but it would have been everything but enjoyable for the blown up assault mechs. They just immediatly died by the roll of the dice.
Plus, from a scientific standpoint, I'm pretty sure a real fusion reactor would simply stop working if heavily damaged and not blow up. Of course I don't know the details about these fictional engines in BT/MW, but I don't think they would argue against the laws of physics to make something like this.
The crit mechanic is already random enough and causing a fair amount of frustration at times, especially together with ammo explosions.
So I personally don't think destroyed mechs should blow up like bombs.
Edited by FunkyT, 27 August 2017 - 08:17 AM.