spickermannI read a couple of message in which people were surprised that Twitter is still online with only 25% of their employees left. Some even argue that those employees must have been redundant because the site is still up.
I once was the last developer of a small startup and was let go when it ran out of money.
My experience: It is possible that web apps run for years without any maintenance. Some feature might stop working, but it can take years before an application finally dies.