Most of these EHSIs display your current ground track.
These electronic HSIs (EHSI) like the Sandel SN3308 and the Bendix/King KI825 were common retrofits for mechanical HSIs.
Being just a display, an EHSI relies on a remote heading gyro and magnetic slaving system--typically the same ones that fed the mechanical HSI.
In some cases, the EHSI display will X-out the heading data when the heading feed becomes invalid, but the typical installation did not provide a backup.
These include a PFD showing all the basic flight instruments including the EHSI (with enhancements) and optional (Aspen) or included (Garmin) multi-function displays for ancillary data and moving maps.
For instance, the EHSI within the Aspen PFD relies on a remote sensor module (RSM) for heading resolution.