The Cubs are in very good position, obviously, even on this road trip. LA is a good team and they've been playing well and they have Kershaw going tonight against Hammel, but then the Cubs have advantages in Lester vs. Latos and Arrieta vs. Wood. I would think an LA sweep is unlikely and the Cubs have a fair chance to win the series, which would give them a .500 West Coast trip. In my book, a .500 trip out there would be a big win.
I've certainly seen my share of Cub disappointments, but at this point, the Cubs have a 5.5 game lead in the WC over SF and the Nats are probably about done at this point being 9 games out. Cubs have 36 games left and the Giants 35. If SF goes 25-10, finishing really hot, the Cubs only have to go 21-15 to keep the WC spot. SF's reality is probably going to be less than that. If the Giants go 20-15, the Cubs only have to go 16-20 to hang on. Tough games coming up against STL, PIT and KC (one game only), but SF has this weekend against the Cardinals and still has 7 against the Dodgers, even if they do get a good number of games against NL also-rans.
The Cubs are guaranteed nothing at this point, but they've earned a nice cushion and SF has a lot of work to do to catch up.