it will burn your valves, your rings may overheat. diesel fires at a lower temperature so it is not designed for that amount of heat in the cylinder.
if you syphon off 95%min of the petrol and change the fuel filters ect it could be salvagable, assuming you have not driven it far, older diesils are much stronger than new aluminium head diesels
depends a lot on how far you got, wether there was any diesel in it to start with..The recovery companies get many callouts on this issue...Usually its drain the tank and refill, filters are recomended to be changed...any real damage is to pump seals actual engine damage is very rare.
My son inlaw done it on a 307 during the summer, cost was about �250 inc.tow in drain and a new tank of diesel this was on a sunday in Devon. The fuel was not changed and its driving around fine 6 months later
in theory you cant put diesel in a petrol vehicle, diesel nozzle is larger.
really depends what the mix of fuel is as to any damage, usually gets spotted before getting to far, ie, smoke, poor running.
i work in the motortrade and as yet never seen a wrecked engine due to wrong fuel.