from your post it is not clear, which train it's for, if for Rajdhani or Duronto, then therz no chance, you will not be allowed at any cost.... but if normal M/E train, thou as per rule you are not supposed to board a reserved coach be it SL,3A or 2A, but on humanitarian grounds, tte may allow you to travel if he feels you can be accommodated en-route, however it will be totally the discretion of TTE currently on duty and TTE's joining enroute.