Answer: What you describe in terms of symptoms sounds like a root problem to me. Either drought stress or overly wet soils will kill the roots which will in turn cause the tops of plants to begin to die down. Without inspecting the root system I'm not sure how to advise you. If the plants have not had enough water you may be able to help them recover by putting them on a regular watering schedule. If the soil they're in does not drain well, they may have developed root rot and no amount of watering will save them. You can dig around the root system to see - healthy roots will be a creamy white inside; dead roots will be either rusty colored or mushy.
I hope this information helps you determine whether or not your plants can be saved!
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