Practical as we westerners are, we have ignored the close combat side of HEMA with the (r)evolution of arms (guns) and by the demand of social changes. HEMA has survived in sports form in boxing, wrestling ands fencing. However there is no known traceable lineage where the art was transferred “unchanged” from master to student.
That said, history has left us with a plethora of excellent sources, archaeological finds and manuscripts describing and depicting the practical use of the art, mentality, governing principles, tactics and strategies.
This of course isn't perfect lineage but neither is a lineage where, as is common, the art is changed due lack of practical experience or by sheer arrogance and self-important feelings of the 'master' of which eastern martial arts can supply plenty of examples.
It is up to us as the HEMA community to keep researching the art scientifically. This means we have to adapt flexibly and fluently as we discover more about it and gain a deeper understanding of the art. We have to remember as we train and use HEMA that new (or rediscovered) understandings will absolutely arise as we work with the materials available, and that those new understandings will require us to adapt our execution of the art going forward.