After much plunging we were able to clear the blockage and the toilet flushes but not able to retrieve the toy (we have no idea what it is). Should we be concerned with a possible blockage in the drain? If so, what should we do?

If the toy has flushed away no problem. If the toy has is still in the line solids and tissue will get caught on it and the blockage will return.

Wait and see.

As said above, once it cleared the toilet bowl, it is somewhere in your house plumbing system, on its way to the City sewer. I would fill tub with water and drain it, all at once. Repeat it. Flush all toilets few times. This amount of clear water should push the toy from your sewer system all the way to the City's sewer. Milo