OK, so if you're asking this, there's no way you've done a proper disaster recovery plan--folks that have done those have sufficient documentation in-hand that someone else should be able to pop in and do the job.
So this is a great opportunity to do that. Together. You gain confidence in your IT minion while s/he gains confidence that they're flying right. And any keys to the kingdom are nicely stored where they should be, so any authorized IT person can get at what they need.
The first step is to get the lay of the land and prioritize services. Gather the keys/passwords/whatever together (make sure your AAA story is good, etc). Come up with what your backup/restore stories are. What do you do if you need to restore one file (the "oopsie" moment)? What about a dead drive/server? What if a plane hits your data center? etc, etc.
Make no mistake--you're in the middle of a disaster RIGHT NOW. You're losing your lead IT staffer to promotion