People often (mistakenly) think that there is nothing that can be done unless “things get really bad.” Actually, there is a lot that you can do to plan in advance.
As an alternative to a guardianship (or a temporary measure before a guardianship), powers of attorney may be what is needed. A person who is able to understand what s/he is signing may decide to name someone they trust to manage business and personal affairs, and medical and health needs.
A person who is able to understand what s/he is signing may also choose to sign a document that names someone “to be my Guardian if a Guardian is ever needed for me.”