What changed: the harbour district still has value, but the exposed walking section no longer does.
Drop first: the longest waterfront connection.
Keep: one harbour-side museum, food stop, or indoor attraction that gives the district a clear purpose.
Check before leaving: what is open now and how you will get back without building a second exposed walk.
Reykjavík plans usually go wrong by keeping too much, not by starting with too little. When wind, rain, a late check-in, or tired legs cut the usable day, protect one good main activity and remove the part that creates the most movement.
This is a drop-first list: seven common situations, the piece I would remove, and the part I would keep. Check the live weather, opening hours, and transport before leaving.