This is an example of an application level add-in that would prompt a user to save if they need to when launching dynamo.

PrompForSaveApp.cs

#This code is proudly provided under the BSD-3-Clause, https://opensource.org/licenses/BSD-3-Clause
using System;
using Autodesk.Internal.Windows;
using Autodesk.Revit.DB;
using Autodesk.Revit.DB.Events;
using Autodesk.Revit.UI;


namespace PromptForSaveOnDynamoLaunch
{
    class App : IExternalApplication
    {
        //the current document
        private Document _currentDoc;
        public Result OnStartup(UIControlledApplication a)
        {
            //using AdWindows, we are able to see when someone clicks a ribbon button
            //here we subscribe to that event
            Autodesk.Windows.ComponentManager.ItemExecuted += CommandExecuted;
            return Result.Succeeded;
        }

       

        private void CommandExecuted(object sender, RibbonItemExecutedEventArgs e)
        {
            bool wasDynamo = e.Item.AutomationName.StartsWith("Dynamo", StringComparison.OrdinalIgnoreCase);

            if (wasDynamo)
            {
                TaskDialog.Show("Hi", "You launched Dynamo. PLZ SAVE. KTHXBYE.");
            }
        }

       

        public Result OnShutdown(UIControlledApplication a)
        {
            //unsubscribe from the event
            Autodesk.Windows.ComponentManager.ItemExecuted -= CommandExecuted;
            return Result.Succeeded;
        }
    }
}