Complex sentence: The last died in 1935 leaving an only son, Mir Faiz Muhammad Khan II, who had suffered from an unstable and nervous affliction for many years--so much so that he could not be trusted with the management of state affairs.
Split into simpler sentences: The last died in 1935 leaving an only son, Mir Faiz Muhammad Khan II, who had suffered from an unstable and nervous affliction for many years. So much so that he could not be trusted with the management of state affairs.