What references to Sombra exist in the game now

If you see a Lifesaver footnote in the PoTG screen, this is intended to feature situations where one player is able to save another player (or players) from imminent death. For example: If Reinhardt has an enemy pinned, and that enemy's teammate stuns or kills Reinhardt, the teammate would be awarded a large amount of "Lifesaver" score. If Mercy has 5 of her teammates downed, and casts her ultimate, the same situation would apply and Mercy would be awarded a large amount of "Lifesaver" score as well.

From the Overwatch wiki:

The player who has the highest score in any one of these four categories at the end of the match will receive the Play of the Game. If the winning Play of the Game category is Lifesaver, Sharpshooter, or Shutdown then the category name will be called out during the highlight intro. If the winning category is High Score, however, no callout will be provided.

From an interview with Michael Chu, a Senior Game Designer on Overwatch (emphasis mine):

If you look at a game like World Of Warcraft, the Horde/Alliance split is such a big deal and such a defining aspect of the game. But Overwatch, pretty much from the start, we didn’t want to restrict ourselves that way. Because the game is so much about having the flexibility to play all these heroes and finding all the ways they play well together or against each other. Because of that we decided that the gameplay of the Overwatch universe wouldn’t be bound by that.

Our story justification – what I usually tell people – is that I think of it as, it’s clearly not canonical, but I think of it as how in comic book stories sometimes Iron Man and Captain America fight each other. Maybe in this instance on this map they’re fighting – for some reason they have some ideological difference or something that’s bringing them against each other.

But I think ultimately it was important for the game that you were able to play whatever characters you want. Blizzard has this development philosophy which is ‘Gameplay first’ and this is definitely an example of where we’ve gone with that.