It's not clear (a lot isn't), but I'd say no. If at the end of the amnesty period (April 30, 2022) you haven't turned in the firearm, and you don't already have a prohibited license, you no longer have the benefit of the amnesty and you are a criminal. There is one other choice - you can render the prohibited weapon not a weapon by "deactivating" it, that is, rendering it impossible of firing, permanently. In that case, you can hang on to it, but only because it's not a weapon anymore.
I don't believe there is an expectation that any new prohibited licenses will be issued. That book is long closed.
I also think, by the way, that it would be hard to "find one on the list" if you don't already have one. The regulatory analysis prepared in connection with the new regulation (they do think of everything) says:
The Amnesty Order has been made to protect affected individuals who (1) were in legal possession of a newly prohibited firearm or prohibited device at the time the Regulations came into force, and, (2) continue to hold a valid licence during the amnesty period, from criminal liability for unlawful possession of a prohibited firearm
So if you don't have one now, you really have no legal option to get one. If you can read the minds of politicians, you can always try to find what they plan on banning next, and get one of those before they do ban them. The regulatory analysis to the new regulation further says:
There is also a risk that affected firearms owners may elect to replace their firearms with models unaffected by the ban, causing a market displacement. This risk may be mitigated by adding additional makes and models to the list of prohibited firearms in the future.
This goes to my earlier point that the government can add any firearms to the list any time it wants, without any further authority from Parliament, because Parliament gave it that authority.
If it will help you to rest more peacefully, you should know that the government performed a "gender-based analysis +" as part of this. Boy, (or maybe girl?), do I feel better.