If it remained open source I`d see no reason to panic yet, that is the single most important part. Though having read through so many posts I'm still not sure if that is the practical case for the FF addon I care about.
I have to look at the alternatives again. I would be fine using Proton for this, but ProtonPass has a couple of issues still. I'm guessing there is no usable free password manager outside of these two, that has a FOSS client doing client side encryption paired with free cloud storage for the passwords. I'm not completely against self hosting, but it would be inconvenient, I'm not going to keep a PC online just for this when I'm not home.
edit:
Bitwarden continues development of open source code under GPLv3. Code under the commercial license is just as viewable and transparent on GitHub. This licensing model provides additional legal protection for select features.
I suppose I can ride this out for a while longer then.