I wouldn't worry about it. Here's why:
If your answer is a link answer, it shouldn't exist anyway. Link answers are frowned upon for the exact reason that you list: that the link can rot, and possibly vanish without a trace, and without anyone knowing. Links are like helpful ghosts: They'll support your argument, then vanish.
Since most good answers on the site should not point people to a link, it shouldn't be an issue. Answers should include quotes, informative content based on experience and the like. Links are present to help support an argument, to attribute to a source... etc.
Whatever it is, don't force people to use services such as the swayback machine or anything. There's no use in the extra step anyway, and if information updates on the linked site, you miss out on anything new.
Link rot isn't really an issue you should be concerned about. You should only be concerned if you've got a site, which is just pointing to other site, and boy is that never happening on something like Stack Exchange :)
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