static map<id,id> beforeUpdateMap;

public static void handleBeforeUpdate( list<Account> newAccounts){

    set<id> actIds = new set<id>();
    for(Account a : newAccounts){
        actIds.add(a.id);
    }
    list<Opportunity> opps = [Select id, accountid, ownerid, owner.name from Opportunity where accountid in :actids];
    beforeUpdateMap=new map<id,id>();
    for(Opportunity o : opps){
        system.debug('***Opp owner on Account beforeUpdate:'+o.owner.name);
        beforeUpdateMap.put(o.accountid,o.ownerid);
    }
}

public static void handleAfterUpdate( list<Account> newAccounts){

    set<id> actIds = new set<id>();
    for(Account a : newAccounts){
        actIds.add(a.id);
    }
    list<Opportunity> updateOpps = new list<Opportunity>();
    list<Opportunity> opps = [Select id, isClosed, accountid, ownerid, owner.name from Opportunity where accountid in :actids];
    for(Opportunity o : opps){
        system.debug('***Opp old owner: '+beforeUpdateMap.get(o.accountid));
        system.debug('***Opp owner on Account AfterUpdate:'+o.ownerid);
        if(o.isClosed && o.ownerid != beforeUpdateMap.get(o.accountid) ){
            o.ownerid=beforeUpdateMap.get(o.accountid);
            updateOpps.add(o);
        }
    }
    //SET A TRIGGER FLAG to prevent ANY and ALL triggers from firing on the Opportunity Update
    //id triggerFlags.ByPassOpptyTrigger=True
    //  and in the Opportunity Trigger, always check this flag.
    update updateOpps;
}