i wouldn't personally think about dumping a batch until i was sure it wasn't good. that means riding it through fermentation, and bottle conditioning, AND a long aging period in bottles if it needed that. sometimes a beer with off flavors can take a really long time to turn the corner and become drinkable.
i brewed an english IPA last spring that got really warm for the first day, like high 70's warm.... it was AWFUL going into bottles, hot booze, loaded with esters. after 4 weeks in bottles, it was worse. i shelved it and forgot about it until about a month ago. chilled a few off, cracked one, and while the hops had faded, the beer had really turned around. it's by no means the best beer i've made, but it's a serviceable beer that i don't mind drinking.
long story a bit longer, don't dump beer unless you KNOW there's no hope.... and any beer in the fermenter has hope, if you ask me.
good luck.