Why is there no conjunction between 健康 and 有活力的生活状态 in 无法保持健康有活力的生活状态?
Your translation has the right idea. It reads something like this:


  Those who don't take care of their own physical well-being will be unable to maintain good health and vitality in their later years, leaving themselves with regret and causing pain to their friends and family.


The bold part can be made clearer, for example like one of the following:


無法保持健康、有活力的生活狀態
無法保持健康而有活力的生活狀態




The reason why it's not clear is because it is a vernacular/spoken sentence written down literally (which you can tell because the sentence begins with「那些」; formal literature does not do this). It is discouraged to write like this unless someone is being quoted verbatim, because such sentences require more effort to interpret when read.

During transcription, the necessary conjunction (or enumeration comma) was simply left out. If you hear the original person saying this, however, they might have inserted a pause, or dipped the tone slightly, between 健康 and 有活力, making interpretation much clearer.