It seems like the OVP suddenly failing can cause a stall like this, there are even bulletins out for certain vehicles which state that intermittent stalling can be caused by the OVP (although I don't believe the bulletin I have in mind covers 126 chassis). But remember that the engine can in fact run without the OVP or even without the engine control unit (not really well, but reasonably well, in what is called "fixed operating mode"). I believe it's the sudden change from running in closed loop to running in fixed operating mode which causes the stall. If your warning lights for ABS is not presently lit, the OVP is probably fine right now. If the ABS light has been lit ever since the stall, you are probab;y in fixed operating mode, which is most noticeable at a cold start.