Why would you cancel IFR? Operating visually clear of terrain and traffic is a perfectly acceptable IFR procedure. Hell, you can even request a VFR climb through class E if you have VMC. No need to throw away your surveillance and SARwatch services.
Don't cancel it, no problem. You can still operate in the way I laid out.
The important thing that’s relevant to this accident and class E is that the Seminole would not have been given a clearance on the ground to depart if there was overlying class E. In class G they should’ve been given traffic but they weren’t.
'would not' not necessarily. Depends if a procedural clearance could have been issued.
'but they weren't' oh yes they were given traffic. It's the timing of the traffic delivery and the airspace limitations that will be subject to a fair amount of scrutiny in the investigation. You'll just have to wait until 2023-ish to find out.