Create a SQL script that will restore your diagrams created in SSMS.

Backup SQL Diagrams.cs

//Specify a filename location if you want to save the file.
string filename = null;
//Set this to a DbSet, DbTable or whatever you are using to access [dbo].[SysDiagrams] for your database.
var sysDiagramsSource = Sysdiagrams;

var diagramDefinition = from diagram in sysDiagramsSource
select new
{
	Name = diagram.Name,
	diagram.Principal_id,
	diagram.Version,
	diagram.Definition
};

// These bytes don't seem to exist in the definition when you select it, but are needed when creating?
// Failing to append these bytes results in an error 
var footerBytes = new byte[] {
	0, 0, 0, 0, 0, 
	0, 0, 0, 0,	0, 
	0, 0, 0, 0, 0, 
	0, 98, 136, 82,	20
};

var footer = BitConverter.ToString(footerBytes).Replace("-", "");

var bytesPerLine = 96;
var diagramSqlQueries = from d in diagramDefinition.ToList()
	//Split the definition over many lines, Many IDEs don't handle unbounded horizontal scrolling well.
	let definition = BitConverter.ToString(d.Definition.ToArray()).Replace("-", "")
					let splitDefinition = string.Join("\\\r\n", Enumerable.Range(0, definition.Length / bytesPerLine).Select(i => definition.Substring(i * bytesPerLine, bytesPerLine)))
					select $@"
exec dbo.sp_creatediagram
	@diagramname = '{d.Name}',
    @owner_id = null,
    @version = {d.Version},
    @definition = 0x\
{splitDefinition}\
{footer}";

foreach (var diagramQuery in diagramSqlQueries) {
	diagramQuery.Dump();
}

if (filename != null)
{
	File.WriteAllLines(filename, diagramSqlQueries);
}