There are several synonyms for the phrase "I hope not". One of the most common is "hopefully not". This phrase indicates that the speaker is expressing a desire that something does not happen. Another similar phrase is "let's hope not". This implies that the speaker and the listener share the same hope. Another way to express the same sentiment is to say "I pray not". This phrase has a slightly more religious connotation. Finally, some people might choose to simply say "no", although this can be perceived as more abrupt and less polite than the other options. In any case, there are many ways to express the sentiment of hoping that something does not occur.