this can be done in two ways.
1. Use TortoiseSVN to restore the deleted branchline.
Or do the following:
1. Create a new branch from the same revision as the deleted branch, open the new branch on the modeler.
2. Close the modeler.
3. Now go to the branch location and delete all the files and folders except the folder .svn and .mendix-cache.
4. Copy all folders and files from the deleted branch folder (except .svn and .mendix-cache) to the new branch.
5. Open the project in the modeler and commit.
6. Merge from the new branch to main.