It depends on your own emotional reaction to the losing streak. If you find yourself getting annoyed and angry, that's the point to stop; you'll play more sloppily, which will make you likely to continue losing, you'll be more inclined to simply blame your teammates and not examine your own play, which will inhibit your improvement, and, well, if you're not enjoying playing the game, then there's no real point in doing it. If you can remain calm and treat each game individually, however, then I think the best way to improve is to keep playing and learn to look at trends in terms of dozens or hundreds of games, not just the last five or ten that you played.