The sentence contains two moods: indicative and imperative. The indicative mood is present in the first part ("Let's go to the mall"), which states a suggestion or fact. The imperative mood is suggested in the phrase "would you rather," which is phrased as a question and implies a request for preference.
To correct the shift in mood, we should unify the sentence into a single mood—either by framing both parts as suggestions or both as questions. Here are three simple sentences that could convey a consistent mood of suggestion:
- Let's go to the mall.
- We could shop online if you prefer that.
- How about we decide together?