Does this create a scenario where all users must transfer their Bitcoin holdings to these new quantum-resistant addresses?
Yes. All Bitcoin holders will have to generate keys that are quantum resistant and transfer their coins.
Moreover, the consideration arises regarding the implications for dormant Bitcoin holdings, such as those belonging to Satoshi. Without an entity to initiate the transfer to these fortified addresses, does this proposition imply the eventual reactivation of dormant bitcoins?
Probably. If Satoshi does not transfer them to the future quantum safe addresses, then they'll end up being stolen.
Will all "lost" coins eventually be reclaimed by the advancement of quantum computing?
Depends on the definition of "lost". Not all lost coins can be reclaimed. Coins sent to public keys whose private keys are considered "lost" by their owners, can be reclaimed. Coins sent to addresses which haven't revealed their private keys cannot be claimed by solving the ECDLP (as with the former), until they spend their coins and be forced to reveal it. These coins' vulnerability to being claimed will depend on how quickly the attacker can solve the ECDLP. For example, if they can solve it in less than 10 minutes, then they could double-spend your transaction while it is unconfirmed.
I'm not the best person to discuss quantum computers, but to alleviate your concerns, I believe that by the time they pose a significant threat, people will have already transitioned to quantum-safe algorithms years in advance.