Harrison probably had the complete data from the company ready to go for any purpose. Maybe it was released with a deadman's switch or by a friend after he got suicided.
I don't think OP is suggesting they might have murdered him in retribution for the hack. As the article describes, there was quite a lot of animosity between the contractor Harrison and the owner of Ashley Madison, including a harassment campaign from Harrison that started two years before he killed himself and three years before the hack.
