1) Someone please correct me if I and wrong on this but the default is R2H with DroneDeploy, however if it loose connection mid mission it should still carry out the mission and then R2H or Orbit depending on which option you selected during planning. I also believe it defaults back to whatever option you set up in "DJI Go 4" app if there is an issue with the mission file.
2) The short answer to this is just don't let your controller ever run out of power as it acts as a battery pack for the tablet while connected. I have flown almost 2 months on one controller charge (at least 2-3 times a week) and never needed to charge so it should be a VERY unlikely scenario. However if worst comes to worse I believe the last part of my first answer still rings true in that it should follow the emergency protocol set up in the "DJI Go4" app
Hope that helps at least a little and Happy and Safe Flying!