1) IE11 correctly handles `@support (display: grid) {}` (in that it recognizes it does not support it, because IE11's spec-inconsistent implementation is prefixed), which means CSS feature detection for grid works and is easy.
2) IE11 has an -ms- prefixed implementation of grid, it's just somewhat inconsistent with the final spec. That said, it's also rather feature complete comparatively, so if you must support IE11, and must give it grids, there is an option to use IE11's native grids as a terrible fallback.
3) Windows 7's extended support ends January 2020. There is less than two years left of security patches left for Windows 7. If your company isn't already planning to migrate to something more recent than Windows 7, time is ticking.