First of all, I have to start by stating that every business should have a disaster recovery plan in place for such an emergency.  If you don't, do it now before a disaster strikes.  Make sure you have all your business data backed up securely on local storage, such as a file server, or NAS (Network Area Storage).  Then ensure all of that same critical data is backed up off site, such as cloud storage.  The local storage is quick to recover data from accidentally deleted files, or a damaged or stolen PC by recovering the data to a new computer very rapidly.  The remote back up is intended for use if your local storage fails, or in the case of a natural disaster where your entire site is destroyed.  The insurance will rebuild your building and assets, but what about your customer files, and company data.  That's what the remote storage is for.  

Your network should also have redundancy or a back up plan for your critical systems if a portion of your network goes down.  So if you have these backups and redundant networks in place, you should not experience any interruption to your business network ideally.  Redundancy is expensive, and many times difficult to design to cover all scenarios, but having a plan in place will relieve some of that stress when that "Situation" arises.  Then your biggest decision may be how long do you attempt to recover the failed system before enabling your "backup or disaster recovery plan".  That decision can be made logically by the estimated amount of down time your company experiences, with the goal of always being the minimum amount of impact time as possible to your business. 

Back to the question: So if you don't have a disaster recovery plan, your only choice is to work on the system until you get it recovered, and call in all the experts you need to accomplish the goal.  Because the longer you delay, the more impactful it will be to your business.