A dead Elise inherently implies that the Insidious franchise can only use her in stories that take place before Insidious Chapter 2 (which is exactly what the studio did with Insidious Chapter 3 and Insidious: The Last Key), but handing off the franchise to Imogen Rainier would drastically open up the timeline and allows the series to produce new sequels unhindered by story constraints.
Most Insidious fans likely already know that canonically speaking, Elise Rainier has a particular endpoint on the franchise timeline.
She dies in Insidious Chapter 2, which means the two subsequent sequels take place before the events of the first film.