In my opinion when player drops out of the game he/she generally does crap. Unless late in the game I will often abort the game because of that. Not speaking of other reasons, dropping out brings decent misrepresentation to the stats.
Yes, dropping in general often changes the game balance drastically, and an extra bonus tile usually isn't among the real issues caused by a dropping player. Some of the main issues are: - another player on a neighbor color gets easy and uncontested hexes which normally would have been taken / threatened to be taken by the dropped player - the dropped player was in a position to do well/win on network, or cults, so depending on when the drop occurs, another player can grab a cheap "unearned" lead - if the drop happens early (in round 1): a player loses the main "leeching mate" and potential neighbor for cheap TPs (e.g. one of grey+black on the eastern continent drops)
You can of course try to convince the remaining players to abort the game, but their decision will likely depend on how much they already invested into the game (e.g. I would support such an abortion if the player drops in round 1, but would not if the drop occurs in round 5 or 6).
...and for TM Tour League games... well you just have to live with it and hope that it doesn't affect who wins the league. In my 1st season a player resigned during faction picks! Since he did it at this time it was fine since the remaining six players all had exactly two 3 player games.