When the diode fails, it can just stop working or get hot enough to melt the
wires or even pop a hole in the
wire .
So at a rough guess this is what has happened & the DPO has cut the section out and just carried on using the mower as the alternator is not needed except to recharge the battery.
If the mower is in good tune you get better than 100 starts from a good mower battery, more than enough to mow the grass then pop the charger on between uses.
There are several customers in my clientele who do just that and even more who jump start of their car because they are too tight to fork out the $ 100 ( aus ) for a new battery .