As to yeast viability;
Bobby M recently did a test on year old stored yeast here;
https://www.homebrewtalk.com/f13/testing-limits-yeast-viability-126707/
And my LHBS cells outdated tubes and packs of yeast
dirt cheap 2-3 dollars each and I usually grab a couple tubes of belgian or other interesting yeast when I am there and shove it in my fridge.
and I have never had a problem with one of those tubes. I usually make a starter but I once pitched a year old tube of Belgian High Gravity yeast directly into a 2.5 gallon batch of a Belgian Dark Strong, and after about 4 days it took off beautifully.
I am going to give you all my standard rant about how, for the most part, the idea of "bad yeast" is really bogus....
Of a dozen or more starters and yeasts harvests, I have only had one that ever krauzened, and NONE that never took off,
given enough time and patience.
Of god knows how many batches of beer I have made....
I have never had fermentation not start, or a beer not turn out ok, and I have never ever ever had to add more yeast to a beer.
Except for infecting a starter due to poor sanitization, it really really is hard for yeast NOT to do what they do naturally.
That's how we can make a huge starter from the dregs of a bottle of beer...we let the viable (living) cells reproduce, and we feed them incrementally, and they continue to reproduce.
Seriously most LHBS know enough about what they are doing in terms of proper yeast storage, same with suppliers, it doesn't take a genius these days to know how to stick liquid (and dry yeasts usually) in a fridge, and ship in bulk in a styrofoam cooler.
We're talking billion dollar corporations (the yeast labs, and that's what they are LABS) and they aren't going to risk their rep by letting their suppliers and stores that carry their stuff , handle it improperly.
Besides...Yeast IS hardier than most newish brewers wanna give them props for...I mean You can't say that THIS YEAST was stored "properly" and yet, they managed to make a batch of beer with it.
45 million year old yeast ferments amber ale
If we can make beer with that....even the tiniest viable glop in a barely smacked pack, is going to work as well. 
Gang I can't say this enough;
Unless you bought liguid yeast through the mail in the heat of summer, or added your yeast into boiling wort. your fermentation will happnen.
Yeast just don't not work anymore, that is an idea that came from the bad old days before homebrewing was legalized in 1978 when yeast came in hard cakes that travelled in hot cargo holds of ships ...And then sat under the lid of blue ribbon malt extract for god knows how long on grocery stores shelves.
But since 1978 yeast science has been ongoing and the yeasts of today, wet OR dry are going to work in 99.9% of the situations we have, if you give them the time to do so.
But every noob who starts an "my yeast is dead thread" just really pertpetuates a fear that has come from way back then, they got it from Papazain and other brew books written Thirty or more years ago, and were told horror stories of those yeasts, and it influenced their writing, which influence nervous noob brewers as well.
And then, most of the time, you new brewers then freak each other out!!!! You see an "infection" or "Not fermenting" thread title, or 10 on a given day and most of you don't even read the story behind it...you just see a dozen yeast is f-d up threads...and then believe my yeast has the potential to be f-d up.
But as the guy who answers those questions on a daily basis and finds out that no hydro reading was taken, nor has it been 72 hours, and THEY (not you) ARE going by airlock bubbling- AND when they do take a hydro reading or pop the bucket lid, they see that there was a krausen....and most of the time they actually post back, to say they were being paranoid, and fermentation DID happen.
But to someone who actually doesn't follow up on those threads, they think that yeast is so damn fragile....when it is the brewer's nerves that are.
But Unless you bought yeast through the mail in the heat of summer, or dumped it in boiling wort 99% of the time your yeast will do it's job...no matter what the title of many threads APPEAR to say.
Yeast handling and growing is a science, AND a BUSINESS[EVEN DRY YEAST GANG, they are all grown in labs, not fly by night operations (that's why the whole argument about dry being sub-par to liquid is really idiotic)..and with the internet, and books, and magazines, including this months BYO btw, even the most inbred LHBS employee SHOULD and probably does know how to properly handle and store yeast prior to selling it to you.
So Even if you don't pitch into the batch you planned and go with another yeast, don't toss out that starter. Give it a couple more feedings, wash it and either slant or mason jar it and store it for later use.
Yeast are really tenacious critters, except in the rarest and most extreme circumstances, they will survive, reproduce and work for you. If they can harvest 4500 year old yeast from a hunk of amber, then even a deflated smack pack, or properly stored outdated tube,
will more than likely still have enough viable cells to reproduce into a starter.
I don't know if you know the story of Charlie Papazian's yeast (White Labs "Cry Havoc") or not. He talked about it on basic brewing. The recipes in both Papazian's books, The Complete Joy of Homebrewing and The Homebrewers Companion, were originally developed and brewed with this yeast. Papazian had "Cry Havoc" in his yeast stable since
1983.
He has used it nearly continuously since 83, sometimes pitching multiple batches on top of a cake, sometimes washing or not washing, etc. In a basic brewing podcast iirc last year he talked about how a batch of the yeast after a lot of uses picked up a wild mutation, and he noticed an off flavor in a couple batches.
Now most of us would prolly dump that yeast. Instead he washed it, slanted or jarred it (I can't recall which,)marked it, and cold stored it, and pretty much forgot about it for 10-15 years. He had plenty other slants of the yeast strain, so he left it alone.
Well evidently he came across that container of yeast, and for sh!ts and giggles made a beer with it. Evidently after all those years in storage, the wild or mutated yeast died out leaving behind a few viable cells of the "pure" culture, which he grew back into a pretty hardy strain...which iirc is the culture that White Labs actually used for their cry havoc...because of it's tenacity and survivability.
It really to me, just goes to show once again how really hard it is to f up this beermaking, and that to give the yeast the props they deserve.
