It will depend on your industry and what type of customers you are looking to target. If making the site responsive will cause a strong influx of traffic to the website (i.e. if many of your users are from a mobile device), it may be worth the move. It is important to remember that SEO is a marathon and not a sprint. The long term results of changing your website may be worth the sacrifice of a short lived top ranking.
Whenever the topic of possibly sacrificing current position for future growth potential arises, you must first evaluate how beneficial can a move like this be? Will it attract a market that has been neglected up until now? and if it does drop in rankings how will that affect revenue and are you in the right position to regain your spot on top?
Two important things to remember in preparation of a change like this is:
1. Make backups of your site as insurance.
2. Try to gain as many quality links and boost your social media presence as much as possible before the change. This will help regain the top spot if it does hurt the ranking.
Hope this helped!
