Use exactly this scenario during linetraining..you regain a failed engine,either after volcanic ash encounter,or for any other reason.
What kind of flight profile would you use for the diversion airport approach?...discussion point only.
Having had a birdstrike engine fail after 4 hours,at top of descent when thrust reduced to idle,inducing severe surge,a descent maintaining some degree of thrust may have prevented the surge.
if you really don't know why an engine failed,then fuel contamination is a possibility.....Whatever,..a diversion to overhead a SELECTED airport,then let down,so that in the very worst case,you have a better chance should the unimaginable happen.
All food for thought,is it not..
Safe and happy flying for 2019..