Is there a way when taking my terrain model back to a dtm to force it to not triangulate, and to hold where I have to triangles trimmed and swapped to? Or better yet create a Drainage Project without having to use a dtm?

If you have defined Void breaklines and an Exterior Boundary breakline, there will be the equivalent features in the native DTM. However, Flipped Triangle edges are volatile and will not be preserved.
If you use LandXML and include Triangles, you will probably preserve them, but the resulting DTM may be almost uneditable. If the Triangles import as breaklines, the DTM will be larger and to edit require editing individual breakline, which is a very clunky workflow.
I had a file on one project that had been round tripped between InRoads and Land Desktop. I needed to bring in new surveys and the triangle edges as breaklines made the task almost impossible. Where the survey surface edges were used to create a void in the original file as part of the merge surfaces tool, a bunch of triangle edges were left hanging. In the end, I found it an easier workflow to rebuild the DTM from its source 3D photogrammetry and earlier survey files, brought in to the model using the oldest first and working up to the latest.
But if you need a DTM only for support purposes, the LandXML with Features might be sufficient.

If you have defined Void breaklines and an Exterior Boundary breakline, there will be the equivalent features in the native DTM. However, Flipped Triangle edges are volatile and will not be preserved.
If you use LandXML and include Triangles, you will probably preserve them, but the resulting DTM may be almost uneditable. If the Triangles import as breaklines, the DTM will be larger and to edit require editing individual breakline, which is a very clunky workflow.
I had a file on one project that had been round tripped between InRoads and Land Desktop. I needed to bring in new surveys and the triangle edges as breaklines made the task almost impossible. Where the survey surface edges were used to create a void in the original file as part of the merge surfaces tool, a bunch of triangle edges were left hanging. In the end, I found it an easier workflow to rebuild the DTM from its source 3D photogrammetry and earlier survey files, brought in to the model using the oldest first and working up to the latest.
But if you need a DTM only for support purposes, the LandXML with Features might be sufficient.