Regarding your question about yeast viability - it probably depends a little bit on how long you had the beer stored in the fridge, and how cold you stored it. Assuming you only had it stored for a few days, it's likely you will still have viable yeast left.
I also believe that you have not done any harm by warming your beer. The full keg of beer has quite a bit of "thermal mass", so I doubt it warmed up all that quickly anyway. The warming rate might have some impact on the health of the yeast, but other than that your beer should be fine. Also, I'm sure the beer warmed much more slowly than a yeast pack would when you remove it from the fridge to warm it before fermentation, so I doubt you've done much damage to your yeast.
Now, having said all that, some of the "young and funky" flavors in your beer may mellow with time, regardless of whether or not your yeast is still viable. I often notice my beers improve with a little age - even when they are stored cold. Some of the flavors you are picking up may be unrelated to yeast needing to clean up their mess, as you say. However, without knowing the exact flavors you are picking up, it's hard to know for sure.
In any case, you should be fine. Let it hang out warm for a couple days, cool it back down, and RDWHAHB!
