Does one typically hand over their research work to their lab if they decide to leave academia?
Ideally, all work would be carefully documented and discussed with co-workers in the group before someone leaves. Often times, though, departures are much more sloppily handled.

However, the research group obviously retains an interest the lab notebooks, data, and other work products created while someone is part of a research group. For data retention practices, I would say that "best practices" would include leaving the originals with the research group, while the person who created the data keeping a copy for their own personal records later down the line.