The fact is, it all depends on how you take care 
of them. If you decide to frame them, you are 
cutting their shelf life down(yes, even if you 
use UV glass and acid-free materials). But, if 
you store them in room-temperature, low light, 
relatively dry place, you are bound to have them 
for a long time. I've seen Disney cels from 50 
years ago on Display at art galleries. I once 
asked the owner of Moonstruck Gallery in Las 
Vegas how he kept them in such great shape(I was 
looking for tips on how to frame cels at the 
time). He stated that the owner of the cels had 
them for years in-between the pages of a 
scrapbook. He got them when he went to work for 
Disney's production dept. in the late 60's. The 
guy found the cels during an inventory check of 
the film lab. They had been stored, one on top of 
another, in a small brown box marked "Lady." 
Turns out they were cels and backgrounds from 
Lady and the Tramp. When I heard the story and 
looked at the cels, I couldn't believe it. The 
cels looked brand new. The lines were nice and 
clean, and the paint was vibrant. I aksed if they 
had been restored, and he said no. Apparently, in 
order to sell the type of art he does, he has to 
disclose everything about the art. So, there is 
one answer. I'm sure the materials used today are 
not as superior as those used 50 years ago, but 
one never knows.