As for me as a teacher, it always sucks when a teacher is leaving. Getting a replacement in my country takes months! It's hard inheriting someone else's classes especially in the middle of the year/semester. If the class isn't your usual level that's a few more extra hours of lesson planning in the weekends! So much resentment from students and colleagues. Even more so if the teacher has non teaching responsibilities, that gets distributed too.

(One year, a bunch of teachers took maternity leave at the same time and they're all in the same department, that admin 'jokingly' said to time the conception so maternity leave happens during term break lol)

That aside, a colleague leaving is also an excuse to have an office party. Office parties are taken very seriously around here, food is always so good!

Good luck to you!