A closed question isn't automatically deleted, so the search engines can still find it. You'll just need to click another link to find the answers.

Theoretically it's better to have all the answers in one place instead of scattered about, so that you can compare and contrast them. In practice it's far from ideal. Often a new question will generate a fresh take on an answer, and the diversity would be welcome.

If there's a subtle difference between the "duplicate" question and the older one, you can edit it to highlight the difference. Unfortunately that's hard to do, and you're unlikely to get the reopen votes even if you do a good job.