For many years at Buffer, any time someone moved on we'd backfill their role by default. About 5 years ago I changed my approach: by default don't backfill.

I found that defaulting to backfilling roles meant that the team remained in a maintenance mindset rather than being in a builder mindset. Backfilling means assuming that we should keep things as they are, rather than allowing ourselves to reflect on whether there's another way.

It's always worth seeing how the team adapts to a gap and whether a better way to organize the team emerges. Especially when leaders move on it's worth letting people who are hungry step up before immediately denying them that opportunity.

I'm not saying never backfill, but to give it some time. There may be a more creative way forward. Or a little time may quickly determine that the role in it's existing form is absolutely needed.

If you decide you need more help again, treat it as a new hire, not a re-hire or a backfill. Everyone is different and the organizational structure should always be evolving and adapting to the unique group of people involved.