I do have tomatoes with fruit that were planted in September. I'm still picking fruit and do have blooms but they're not setting any new fruit right now. You're right, the blossoms just drop.
At this time of year, I usually blame the weather - tomatoes set fruit in a range of night temperatures, and if it's above or below those, you get bloom drop. We've had it pretty warm, (and you're warmer) even at night but it wasn't too warm for them to set fruit. It might be the abrupt temperature drops we saw during the holidays, and again this last week or so. I've been covering my plants in hopes they wouldn't go dormant, but I think they have. Going to take a stabilizing of the temperatures to get them going again.
I wouldn't ditch the plants just yet, unless there's evidence of other maladies like browning leaves or something (indicative of a blight or fungal thing going on). They will start blooming and setting fruit again in a month or so.
