Topology doesn't really have a noticeable impact on performance outside of polycount. Everything is triangulated, vertex cache optimisation is applied, etc. Uneven edge lengths and tri sizes can cause issues since they don't play nice with the clustered nature of rasterization (overshading), or more recently, the spatial indices used in raytracing, but outside of that your GPU isn't too concerned with how your topology looks.

The issue, assuming you wanted it watertight (which you might not), would be the resulting normals/tangents. But let's face it, shading artifacts would be a kindness.

Topology doesn't really have a noticeable impact on performance outside of polycount. Everything is triangulated, vertex cache optimisation is applied, etc. Micro-triangles can cause issues since they don't play nice with the clustered nature of rasterization, or more recently, the spatial indices used in raytracing, but outside of that your GPU isn't too concerned with how your topology looks.

The issue, assuming you wanted it watertight (which you might not), would be the resulting normals/tangents. But let's face it, shading artifacts would be a kindness.

If you really wanted it watertight, you could collapse the edges and weld the vertices. Let's face it, shading artifacts would be an improvement.