I know that SEO is continuous, but after a couple of years of SEO, let's say 5 years of link building. Do I need to continue doing SEO, or will the traffic that I got the past years will do SEO for me?

You say "I know that SEO is continuous" which kind of answers the question you later pose of "do I need to continue doing SEO" doesn't it?

Link building is not in itself search engine optimization. Link building as the sole tactic in an SEO strategy is like having some cheap icing for a cake. You got to bake cake man!

And about the other part of your question, the "traffic" you may have received in the past is barely related to the traffic you may get in the future, barely. Traffic patterns are important when establishing trust with the search engine but unless things evolve on site the search engine will lose interest. It wants new stuff from a trusted site, fresh brand new stuff man. Take out the bong and contemplate that for a while then get creating content. Out.

Yes, you are ought to continue SEO. It is a long term process.

Well the answer is yes, If you won't do SEO, your competitor will be on top ..

At the sake of sounding repetitive, yes, you absolutely need to keep up with it. Perhaps another opinion will convince you ;)

Over time, if SEO is not maintained then rankings and traffic will slip. If you are not creating new content and you do not have new links coming to your site from other web pages, your site will be deemed. In order to maintain and grow your search engine results, you have to maintain SEO constantly.

as you said SEO is continuous process..if you stop doing SEO to your site your competitors will beat you. according to me SEO is a never ending process untill and unless closing the business.

SEO is a continuous Job. You have to continue to make backlinks for your website, untill and ever your website is Live.

Yes, SEO is something you should continue to be doing despite how long you’ve been doing it for. It is important to continue SEO so your ranking doesn’t go down. Google looks for indications that the website is still being kept updated and hasn’t been abandoned.