Red brown leaves
When blueberry plants collapse abruptly like this, I think first of water. Too much water will drown root and/or cause phytophthora root rot. This is more likely on heavy soil. Too little water will do the same but is unlikely with live plant right next to this one. The other possibility is a fungal infection in the wood at the base. There are several such pathogens that vary by region. You might look at the wood at the base of the plant to see if there is evidence of a canker.