Starting an exchange (using createrawexchange) is just about creating an offer in a partial transaction, and nothing has yet happened on the blockchain at all. So if that offer is never accepted, that's the end of the matter.
You can also use disablerawtransaction to explicitly prevent an offer from every being accepted. If you don't do this, the assets in the output created by preparelockunspent will be locked (unless you explicitly set the parameter not to), meaning they will not be spent by the node when doing regular operations like sendasset, unless the output is first unlocked via lockunspent.
