Even though specifics are scarce, I'm willing to bet 5G was/is shaping up to be every bit the disaster it seemed like it was going to be, and the rumors that even DiDio was getting cold feet about it probably signalled internal conflict at the company and the higher ups finally pulled the trigger to get rid of him because of it. DiDio just had lots of terrible ideas and was always given few reign despite that. Maybe he finally had an idea so bad the powers that be had to step in...
As to Harras, he was never more than DiDio's puppet. He was arguably the least powerful EiC in the history of the industry. I can't see him sticking around long with his overlord gone.
Now, where they go from here is crucial.