he must have an accident,or he ()here then.应该填什么?

he must have an accident,or he ()here then.应该填什么?

had been
or 是虚拟语气的提示词
must have done 是对过去的肯定推测,表明是过去式
虚拟语气的时态是退后一个时态,那么原来的过去式,在虚拟语气中,就变成过去完成时,had been