TL;DR boycott and publicly denounce Shopify. This situation sounds fairly complex with lots of blame to go around, but it seems that all of the bad faith acts were ultimately driven by pressure from that one company.

Also lesson learned, if you are an open source community then good god make sure that your governance plan is water tight, crucially that any changes to admin membership or permissions be vetted and approved by group consensus first. If one person with an admin role can unilaterally nuke everyone else if they want, then you might as well have both your front and back door completely open to tampering. Reminds me of reddit mod drama.