The fact that you DIDN`T post that the chain was seized up is a good indication that the lube inside the chain hadn`t been washed out completely. Any corrosion on the outside plates of the chain is pretty superficial, but you want to keep the rollers and internals corrosion free.

Two reasons for that: (1) Iron oxide takes up mose space than iron and has a rougher texture. That causes parts to sieze and increases friction on the ones that don`t. (2) Most metal oxides are actually harder than the pure metal and iron is no exception. In fact iron oxide is as hard as a hardened steel file.

So the combination of those will accelerate wear in bothe whole drive system. A chain can be inexpensive, but you don`t want to have to start replacing chainrings and cassettes any sonner than you have to.

WD-40 is a good thing to keep around if you drive in the rain a lot. It displaces water and is easy to apply . As a lubricant its too light weight to last any amount of time, but it can buy you some time and let you do a proper lube when you have the chance.