Of course it's possible, but you will need to find a way to force the flexibility of a document db like MongoDB into a RDBMS like SQL Server.
It means that you need to define how you want to handle missing fields (will it be a NULL in the db column? or a default value?) and other things that usually don't fit well in a relational database.
Said do, you can use an ETL tool able to connect to both databases, SSIS can be an example if you want to stay in the MicroSoft world (you can check this Importing MongoDB Data Using SSIS 2012 to have an idea) or you can go for an open source tool like Talend Big Data Integration which has a connector to MongoDB (and of course to SQL Server).
