How long will it take?
First, understand the size of the downloaded patch has absolutely no bearing on how difficult it will be to recover from it. What matters is the number and types of changes in the WoWclient.
If the WoWclient changes are small, Honorbuddy should be available in half-a-day or so. Typically, patches take from 1 to 3 days to recover. If the patch contains new anti-botting measures, the process can take longer. The longest recorded Honorbuddy down time to date is 15 days to recover from release of MoP . To put that into perspective, your Honorbuddy subscription is 'lifetime'.
Making Honorbuddy 'safely' work again after a patch is BosslandGmbH's highest priority. The product will not be made available after a patch until a thorough analysis of the changes have been conducted, updates made, and testing done.
The process takes as long as it takes--if that's a month, that's what it takes. BosslandGmbH will not jeopardize the account investments made by its customers due to a rush to restore the product to service!