Whether it's worth fixing is really your call. A new Display Assembly will cost a few hundred dollars (check Ifixit.com and/or Ebay). If the only problem is the glass, you can get that for far less.
To get it to work with your external monitor, connect it to the MBP and the MBP to power. Then close the lid on the MBP. It will then display properly on the external screen, provided nothing else is broken. Use an external mouse to control things.
When you've done that, you can set your external display as the default display in System Preferences. Then when you open your laptop again, the display will flicker but the interface with Dock and windows etc. should stay.
I hope that made sense (and that I remembered how this works properly; I'm not at my machine)...