You're still free to use whatever version you're currently using under the terms of the original license.
From an ethical point of view, it's worth thinking about whether you'd like to respect the wishes of the author(s) of the software, even if you are not legally required to.
Do the laws allow for retroactive changes?
In most places, probably not.
A license agreement is agreed to by both parties. If the terms of the agreement change, neither party is required to "re-agree".