Dragon Age: Origins disappeared from Origins game library after uninstall.

What platform are you playing on??  PC, xbox, etc???  How did you purchase the game??  Physical disc, digital download??

Reason I ask, is if it was physical, and an old install on PC, you may have to find it on your disk, and go through reinstall.  If you purchased/activated it on Origin and possibly same on others, there is a feature to Hide games in your display, by clicking on it, or by using a filter to only show installed games.  If it is hidden, then you need to look at the filter options for your library and choose show hidden games, or show all games and it should reappear.  IF by some glitch it is totally gone from your library, then you will need proof of purchase such as an email, the game code, or something of that sort to prove you bought the game.  Once you have that in hand, you need to verify that you are on the correct account...meaning it was actually purchased on that account, and then contact EA support site through chat for PC, and Microsoft for Xbox and so on with the purchase data, and have the track what is going on. 

Usually when a game goes missing, it is because someone logs into the wrong account, meaning they logged into a secondary account when buying, but are now in the primary account and not seeing it.  I have heard on Xbox, you can have a master account for the machine and it lets all accounts playing on that machine play the game...which can cause a similar issue if something changes on the machine.....