Funky Buddha, others

You will definitely lose adjuncts over time. Coffee goes fast, vanilla can vary depending on how much was used, bourbon barrel tends to stick around a little longer. Beers that are well-made on their own -- where the adjuncts actually complement quality base beers rather than cover up flabby ones -- will still be worth drinking even after those adjuncts have faded. I just had a not-even-that-old Ibex Cellar Coffee Stout from Schlafly with minimal coffee hanging around, but the base beer was still excellent and the drinking experience was still very pleasant as a result. Same with Sump.

But if the adjuncts are the draw, even when laid over a quality base beer, you're still best served by drinking it ASAP.

 

I've had Last Snow super fresh to a year old many times. Definitely drink it fresh. All the coffee falls out and loses what little balance it had with the coconut.

 

I tend to do what the lable tells me to do....unless I'm drinking a DFH olde school barleywine. Not burying my beer, lol.

 

I find flavor additions fall off in all cases. Chilis fade fast, so does vanilla it seems. Coffee turns to green pepper flavors. Cinnamon lasts longer from what I've seen.
To be clear, these flavors are not adjuncts. An adjunct is a fermentable that is not barley. Wheat and oats are adjuncts, coffee and cinnamon are not.