We keep Ashkenaz minhagim. My husband thinks he read in the zohar that it’s an inyan for all the people listening to kiddush and havdala to say l’chaim after the person making the kiddush/havdala says savri maranun. Is this considered a hefsek?
It is true, and this is the reason the Sefardim say it by kiddush. It is not a hefsek because it is said before the actual bracha is said. As a side point, a person should be careful not to change their minhagim, especially regarding kiddush. According to kabbalah, there is a significance to the amount of words said in the kiddush, and different communities have different ways how to calculate this. If you are going to do part of one type of minhag and part of another you might end up not doing like any type of minhag.