The phrase "slow death" means a long and agonizing process of dying or a situation that gradually becomes worse and more unbearable over time. Full definition
They witnessed many slow deaths of cats who were severely injured. (catwelfare.org)
They combined decent big - play prevention with the worst efficiency in the country, and they were subjected to slow death on a weekly basis. (sbnation.com)
I've been doing some work of late with a very significant publishing client, trying to understand the reasons behind the painful slow death of a product. (slaw.ca)