Well, isn't this statement of theirs just that, a notification that they are starting work on the service? I believe they are also aware that if they are offline, will not be able to work and will not make a profit.
I see it the same way. Such an announcement is also not atypical for an online service. You also see this from time to time with online banking systems or exchanges.
The only unusual thing is the duration of the service outage. However, this strongly depends on how big the development team behind Sinbad is and how serious the changes are. If, for example, they have to change their server provider, then such a downtime can last for days.
Will this affect Sinbad's campaign too?
We'll know on Thursday when it's payday. It is in two days.
Patience is the key, even if I would like to know myself whether and in what form the campaign will continue.