I assume the same principle applies as for a firm that uses a mixed (debt and equity) capital structure and whose projects don’t meet the WACC threshold / the project’s return is below the IRR of the firm. The overall firm value decreases and hence the project shouldn’t be accepted and the share price would be likely to decrease. However, even though a project may have a negative NPV, it may be one worth taking if the option it provides the firm (to take other projects in the future) provides a more-than-compensating value.