I believe that Arius had been restored to good graces when he was poisoned with an intestine damaging abrasive, causing him to first have extreme abdominal pain then when running off to relieve himself, hemorrhaging out the anus and finally dying from loss of blood. This can be attested to from eyewitness accounts.
Athanasius was a hierarchical tyrant with an ax to grind. I would not put it past him to have Arius poisoned.