On resuming from suspend today (with Xubuntu 16.04), suddenly most of the characters on my screen turned invisible (or, same as background  colour), so I tried logging out, at which point I got the message that Desktop had crashed. Due to the text being hard to read, I believe I managed to hit "save session" before logging out. 

On logging in again, I had no desktop, though everything else worked fine. It took me a while to figure out what had happened. The workaround was of course to Alt-F2 and start "xfdesktop", saving the session one last time before logging in again, but this was quite confusing for a while, and I doubt less technical users would have figured out what to do.

I understand that session saving is used as a poor mans desktop-manager-selector, in case power users want to run something other than xfdesktop – or nothing at all – but perhaps there could be a friendlier way to help Normal People who get into this situation? (In my experience, these "rare situations" happen all the time to people who don't have the know-how to IRC their way out of them.)

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One possible suggestion: On login, the program that starts the session checks if xfdesktop is listed there. If it is not, and the file ~/.config/xfce4/no_dm_ok does not exist, the user gets a dialog

----------------------------------------------------------------------------------
| The Xfce Desktop was not listed in your session, did you really want to log in
| without the Xfce Desktop running? 
| 
| [ No, start the Desktop ] [ Yes ] [ Yes, and don't ask me again ]
\_________________________________________________________________________________

where choice #3 touches  ~/.config/xfce4/no_dm_ok. 


(Perhaps there's a specification that desktop managers have to conform to s.t. it could check for "a desktop manager" being in the session instead of just xfdesktop in particular, but I think this solution at least could solve the main papercut.)