Google Ads campaigns can be very effective, but also costly and dig deep into the profit margin of businesses with even relatively large average single acquisition prices. Therefore, it's only a natural and economic question to ask - for how long??
The first thing you must realise of course is that the second your Google Ads cease to run, your website visitors will cease coming as well. There are no freebies, no bonuses or long service rewards for having a three year Google Ads campaign and then stopping it suddenly - you haven't built a foundation in the search engines, you haven't even built reputation with organic Google search results.
Nonetheless, while you benefit from the instant traffic of Google Ads, you must be slowly gathering organic reputation with Google so that visitors from your SEO campaign will soon overtake the number coming from Google Ads.
An effective way to proceed then is to taper off your Google Ads spend, keeping one foot in both camps while you measure analytics, including sales or conversions, and determine when the threshold has been passed where a more effective CPA (cost per acquisition) is coming from SEO than the Google Ads CPA.
Having said that, with some good professional SEO you could be just months away from never needing Google Ads again.
Some sites are in markets that are low-competition or niche due to their narrow field of interest or highly geographic nature. With a properly coded website, you may find you can rank very, very quickly for your desired search keyword without needing any Google Ads to bridge the gap in visitors while your site gains rankings.
As an example, this private chef in Mosman operates in a highly competitive field but in a very localised geography (a single suburb of Sydney). While it's a popularly targeted suburb (for any type of advertising, from Chefs to Kitchens to Pools to Pooch Pamperers), our client was able to dominate rankings for several keywords as soon as her website was ready... even the 'under construction' page we immediately placed for her while she gathered her images was enough to launch her to the first page of Google!