I think the most demotivating part of Harper’s job is the lack of recognition (and feedback) for taking on additional workload (although overall communication from management is low and also needs to be addressed.

If I were David’s supervisor and he came to me for advice on how to help Harper feel engaged again (presuming David noticed on his own that Harper is feeling disengaged, which in my read of this case study is definitely not a given), I would suggest he set up regular recurring one-on-one meetings with Harper (somewhere in the once a week to once a month range) to discuss her current workload, positive and constructive feedback, and what her progression options are (including what she needs to work on to be promoted). I would strongly recommend David assess whether Harper’s workload is reasonable, with the goal to reassign work as needed (and being careful not to take away the interesting projects and leave her only with the less engaging/less promotion-oriented work). He should also stress that his door is open for any discussions Harper needs/wants to have outside of regular meetings.

There are several costs to the company in losing Harper: the costs (monetarily) of searching for and training a replacement hire; the loss of institutional knowledge she has; and the demoralizing effect on the other marketing team members when they see a good employee leave because the company appears to not care enough to work to retain her (and the possible catalyst effect this can have if those team members become inspired by this to leave themselves).