You can vote for a new president after the facts at the next election. For being a member for 40+ years it's just crazy that a one-time vote can have this impact on a country

There's nothing crazy or even unusual about it.

Countries typically have one referendum on joining an international organization (the country where I live had a EU membership referendum in 2003) and one on leaving it. It's not a regular or periodic process. Membership in an organization has a certain permanency to it. So you can't be entering-leaving-entering-leaving... every 4-5 years, that's obviously absurd.

Maybe in a few decades, assuming the EU still exists, there will be a referendum on joining it again.

You are just appear to see the issue from the position that EU membership is a good thing, so there should be a vote on "rejoining" it. If the result was "remain", the "remainers" would not be calling for a "recount" or a "revote".