Answer
Wa `alaykum as-Salamu wa Rahmatullahi wa Barakatuh.
In the Name of Allah, Most Gracious, Most Merciful.
All praise and thanks are due to Allah, and peace and blessings be upon His Messenger.
In this fatwa:
Alcohol is not allowed to sell, but your friend can hire the restaurant to anyone though some may wrongly use it as he is not responsible for their deeds.
In response to the question you raised, the European Council for Fatwa and Research (ECFR) issued the following fatwas:
1- Selling alcohol, as well as any other outlawed food or drink, is totally forbidden, even if the merchant refrained from benefiting from their revenue or gave it in donation. One must always fear Allah Almighty in his work and the manner in which he makes his living. Allah Almighty stated in the Qur’an, “And for those who fear God, He (ever) prepares a way out. And He provides for him from sources he never could imagine” (At-Talaq 65:2-3)
One must also firmly believe that lawful (halal) income is blessed, even if small in amount and unlawful (haram) is cursed. Whoever gains from haram sources lives in constant sin unless Allah Almighty chooses to forgive him.
2- There is no objection to hiring your premises as described in the question, as the owner is not responsible for the actions of those who are holding the party. As long as the contract of hire or lease does not involve any haram agreements in itself, it is not the responsibility of the owner to bear the burden of what the hirer does.
3- All drinks that do not intoxicate are halal. Therefore, since the drink described in the question does not intoxicate, then it is deemed halal. It has only been given a despised name which is usually used in reference to alcoholic drinks.
However, the ultimate decision is not tied to names, but to the essence of matters. Further, what is deemed halal to drink is halal to trade with and sell.
Allah Almighty knows best.