Closing channels shouldn't affect this number - these just apply to pending HTLCs afaik and a peer won't forward any more HTLCs once this number is hit (at least this is how I image an impl handles the condition). I might be mistaken but I think this limit relates to how many outputs you can fit into an on-chain tx. Once HTLCs settle, new commitment txs are formed between channel peers, ie theses HTLCs are integrated into their channel balance rather than being a separate output, so they can begin accepting more again.