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That inside corner will need additional support loops to remain sharp. The width of these loops should be similar to the width of the other perimeter support loops. There's a few different ways to approach the topology layout. As long as everything smooth properly, it's possible to use triangles and n-gons to connect the corner support edges to the rest of the geometry. Since this mesh will be used as a base mesh for sculpting it probably makes sense to try and keep everything on a quad grid.

Here's a couple examples of all quad topology layouts that provide additional support for the inside corner. The first example uses a bit more geometry and since the peak of the cut out lands between the segments the topology is compatible with back to front mirror modifier.

The second example uses a bit less geometry but, since there's a quad connecting the edges around the peak, it won't work with a back to front mirror modifier. Both of these topology topology layouts would probably have to be created before sculpting on the base mesh.