Reputable hosting providers typically don't try to quantify such a loss, but rather outright offer a credit/compensation that is very obviously generous (say, a year or even two of free service).

Especially when a small set of your customerbase is affected, it won't cost you that much, and "overcompensating" like that means that virtually noone is going to criticize you for quantifying it wrong; instead, the public narrative will be centered around "well, shit happens, they did their best and generously compensated".