There is no such thing as bug free software, even if your program is 'bug free' its executiuon depends on many factors and elements you will never control like efficiency of computer hardware, network, external libraries, operating system and even users actions. Due to that fact services environment shall be decentralized so we can avoid downtimes.
Centralization by Decentralization
Blockchain can be a revolution but also can cause biggest failure in the history. Many teams are working to develop best blockchain for the decentralized applications so in the future all of the decentralized apps will be runing on the 1-3 most popular blockchains (maybe EOS, ETH and NEO). So to utilize blockchain decentralization feature we will create centralized environment to run applications.
Blockchain blackout
Ethereum network failures that we experience almost everyday in the future may cause that whole world will stop because everything will be runing on the one operating system, that does not sound very well. I know that with time blockchains will have bigger capacity and generally will be more robust but we can never eliminate failure factor in 100%. That is why i think that blockchain technology will survive but not in the current shape, there will not be one global shared blockchain for everyone in the world. Companies will focus on developing their own dedicated solutions on the top of their own blockchains.