Can a person go into"remission" with borderline personality disorder without therapy and/or meds?

One does not go into: Remission when one has a "borderline personality disorder". One can improve tremendously , especially with good therapy, and there are no medication, really, to treat this disorder. One can take medication to control anger outbursts, feeling depressed or anxious but the improvements of the character traits come out of doing "the work" on oneself.

It depends: It depends on the stresses on the person, and the sources of stability s/he has. Many people with bpd are fine with their work, but have more difficulty in intimate romantic relationships. When relied-upon sources of support change or leave, the bpd person may experience a lot of turmoil and need help. Some become suicidal or do other self-injurious behaviors. Therapy is still the best treatment.