Can being bedridden for several months lead to total cardio respiratory failure and destruction of major organs? I know it always causes DVT and PE.

Saddle embolism/pe. prolonged immobility can result in deep venous thrombosis and pulmonary embolism as you mentioned, if the pulmonary embolism is large enough it can cause what is known as a saddle embolus which can obstruct the main pulmonary artery and can result in cardiac arrest.