Formal:
* Nous regretterons: This is the most formal way to say it. It literally means "we will regret."
* Nous manquerons à: This translates to "we will miss (someone)."
Informal:
* On va nous manquer: This means "we will be missed."
* Ça va nous manquer: This is a more informal way of saying "we will miss it (something)."
Examples:
* Nous regretterons de vous voir partir. (We will regret seeing you leave.)
* Nous manquerons à nos amis. (We will miss our friends.)
* On va nous manquer à la fête. (We will be missed at the party.)
* Ça va nous manquer, ce restaurant. (We will miss this restaurant.)
The best way to choose which expression to use depends on the tone and formality of the situation.