No, if you unfriend someone on Snapchat, you will lose your streak with that person. A streak on Snapchat is maintained when you and another user exchange snaps (pictures or videos) for consecutive days. The number of days you've maintained this streak is represented by an emoji next to the person's name.
When you unfriend someone on Snapchat, you remove them from your friends list, which means you can no longer exchange snaps with them. As a result, any existing streak with that person will be broken, and the emoji indicating the streak will disappear from both of your profiles.
If you want to maintain a streak with someone, it's essential to remain friends on Snapchat and continue exchanging snaps with each other daily to keep the streak going.