The best way to cope up with the unexpected situation is to prepare properly. With one of the following cases on hand, you can choose the best solution to save your ost file to a pst format. So pick the case & go for the solution!!
First Case: Your Exchange server is no longer available. Does the Exchange Server go into non-functioning or dismounting stage? Or you just moved your company, and you only have the copy of the .ost file. However, you just realised that unless you have a connection to the Exchange Server, Outlook does not let you open this OST file. If this is the case, then there is no supported method of accessing the OST file. These five OST to PST tools could help you get back your OST file data into PST Format safely and securely.
Second Case: If you have details of the user account that was using the desired OST file & that account still exists within the domain. In this case, you can easily access the ost file to the pst format. For this, you could log in as that user, and then make a COPY of the OST in the path noted in the Data Files path, then make sure you disconnect from ALL the networks, and then open Outlook. From there you can drag and drop to a PST. This method is easy but for this the Exchange Server should be in working condition & the user account must be the ORIGINAL one, not a re-created version.
The other substitute is to back up your data on a regular basis.
This post has covered a list of the best trialware OST to PST converter software packages, considering factors such as: whether or not your Exchange Server is working; you don’t have access to your Outlook profile; and Corrupt OST files (you will be able to open OST file from different Outlook versions). We picked five of the best trialware OST to PST tools in the business. Just pick the one that most closely matches your requirements and your budget.

The purchased full version converts OST files to PST, MSG, EML, RTF, HTML, or PDF. The software helps you to repair the damaged OST file and some severe OST file corruption. Here are some of the helpful features of the software:

The purchased full version converts OST file to PST file quickly and easily. Some of the advanced features of the software are
• Converts OST file to PST file format only
• Supports Outlook 2016, 2010, 2007, 2003, 2002
• Search & Scan Options for OST file
• Automatic software deployment and licensing Feature
• Converts OST file components such as contacts, calendars, etc
Cons
• In some cases, non-default OST file connected to Outlook could not be converted.
• In some situations, only one or no files found after the scanning process completes.
• Does not support password protected OST file Conversion

The purchased full version converts OST file to PST, DBX, MBOX, MSG, EML, TXT, RTF, HTML, MHTML. Some of the advanced features of the software are:
Pros
• User can search and select preferred email items
• Converts OST file data in other file formats like DBX, EML, TXT and RTF
• Converts OST file components like Calendar, Drafts, Notes and Contact lists
• Easy to use GUI
• Allows to save email items from a particular date range.
• Supports MS Outlook 2016/2013/2010/2007/2003/2002/2000/98
Cons
• Does not support to compress & split converted PST file
Systools OST Recovery

The purchased full version converts OST to PST, EML, MSG. Some of the advanced features of the software are:
Pros
• Repairs & Restores OST file into common file types like PST, EML, MSG
• Supports MS Outlook 2016, 2013, 2010, 2007
• View All OST File Messages: Mails, Calendar, Contacts, Tasks
• Converts inaccessible OST file to PST file
• Works for all versions of Windows OS.
Cons
• Does not support to compress converted PST file
• Does not support to convert password protected OST file
• Does not support to convert OST file to DBX & MBOX format

The software is free for the OST to EML Conversion only. The software doesn't support converting OST file to PST format in its free version. The purchased version has the following important features:
Pros
• Export data from inaccessible OST file into PST file
• Can save individual emails from inaccessible OST File
• Can extract data from password protected OST file
• Supports Outlook versions from 97 to 2013 (32 and 64 bit)
• Converts OST file to PST, EML, MSG and HTML
Cons
• Doesn't support converting OST file to DBX & MBOX format
• Doesn't Export OST file to Office 365
Conclusion: I would personally recommend purchasing the full version of Stellar OST to PST Converter to all Outlook users. The purchased version of the software has many advanced features such as deep scan, assurance of no data loss, ability to convert severely damaged OST file & more. Stellar OST to PST Converter is one of the best OST to PST tools out there. Its unique features like - convert OST to Office 365 & split and compact large PST file set it apart from other converter tools.
The User Interface is very easy to use & provides log reports containing detailed information of conversion process along with the ability to preview OST file before converting it.
Have I missed mentioning some trialware OST to PST Converter software? Please mention your suggestions in the article comments.