Colonies can fail over winter. Surveys suggest that about 10% fail in a good year; more in a bad one. At the moment, none of my colonies have failed. I'm happy.
It's too early to be certain that all will survive into summer. Each colony will strike a balance between brood production and foraging. If they make too much brood when the forage is poor, they may starve.
Failure can happen because of disease, starvation or an external event. There are lots of diseases and lots of events. There is only one cause of starvation.
My big event this year (the knock-down during Storm Doris) could have been fatal for the two hives if they hadn't been secured with hive straps. The exposure caused by an unsealed hive would have chilled and killed some of the bees; brood might have died from exposure and consumption of stores would have risen. Instead the damage seems to have been slight. The hives toppled so that the frames were end on (rather than face on). The hive body stayed together. I arrived soon after the event.
Disease does not seem to have adversely affected them. There is Varroa in all five colonies. Four of these are untreated, but were only established last year. One was treated in Spring last year before I resolved to stop. It's too early to be certain that all have become Varroa tolerant but I have reason to hope. There are signs of CBPV and a worrying pile of rotted bee bodies outside Hive D. We'll see how that hive fares.
Even the late swarm in Hive E seems to be ok. I'm optimistic coming into 2017.
: An article published by Thorne in Nov 2016 suggested that weekly consumption of stores by a colony would double if they are disturbed.